Laser processing method

ABSTRACT

A laser processing apparatus provides a heating chamber, a chamber for laser light irradiation and a robot arm, wherein a temperature of a substrate on which a silicon film to be irradiated with laser light is formed is heated to 450 to 750° C. in the heating chamber followed by irradiating the silicon film with laser light so that a silicon film having a single crystal or a silicon film that can be regarded as the single crystal can be obtained.

Divisional of prior application Ser. No. 09/315,968 filed May 21, 1999now U.S. Pat. No. 6,495,404, which itself is a Divisional Application ofapplication Ser. No. 08/504,991 filed Jul. 20, 1995, now U.S. Pat. No.5,923,966

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a technique for subjectingsemiconductors to each kind of annealing by irradiating thesemiconductors with laser light.

2. Description of the Prior Art

Heretofore, techniques are known for subjecting semiconductors to eachkind of annealing by irradiating the semiconductors with laser light.For example, the following techniques are known; a technique fortransforming an amorphous silicon film (a-Si film) formed on a glasssubstrate by the plasma CVD into a crystalline silicon film byirradiating the amorphous silicon film with laser light; and anannealing technique after impurity ion doping, or the like. As each kindof annealing technique using such laser light and an apparatus for laserlight irradiation, there is a technique described in Japanese UnexaminedPatent Application No. Hei 6-51238 filed by the applicant of the presentinvention.

Since each kind of annealing treatment using laser light does not causethermal damage to a base substrate, the treatment becomes a usefultechnique in the case where a material that is weak to heat such as aglass substrate or the like is used as the substrate. However, there isa problem in that it is difficult to keep the annealing effect on aconstant level at all times. Further, when an amorphous silicon film iscrystallized by irradiating the amorphous silicon film with laser light,it is difficult to constantly obtain a favorable crystallinity that isrequired. Thus, a demand has been made on a technique for stablyobtaining a crystalline silicon film having a more favorablecrystallinity.

SUMMARY OF THE INVENTION

An object of the present invention is to solve at least one or more ofthe problems described in the following items:

(1) to enable providing a constant effect at all times in techniques ofannealing semiconductors by irradiating the semiconductors with laserlight; and

(2) to further heighten the crystallinity of a crystalline silicon filmobtained by irradiating an amorphous silicon film with laser light.

A first embodiment of the invention disclosed herein is a methodcomprising the steps of: heat-treating an amorphous silicon film tocrystallize it; and irradiating the crystallized silicon film with laserlight. This method is characterized in that during the irradiation ofthe laser light, the sample is maintained within ±100° C. of thetemperature of the heat-treatment.

In the first embodiment constructed as described above, the temperatureof the heat treatment performed during the crystallization step can beselected to be 450-750° C. The upper limit of this temperature isrestricted by the highest tolerable temperature of the substrate. Wherea substrate made of glass is used, the upper limit is about 600° C.Where the productivity is taken into account, this temperature ispreferably above 550° C. Therefore, where a glass substrate is employed,it is desired to perform a heat treatment at a temperature of about550-600° C.

During the laser irradiation, the heating temperature is preferably setto about 550-600° C. Heating starting from a temperature of about 450°C. can be put into practical use. Accordingly, the heating temperaturepreferably lies in the range of 550° C.±100° C.

A second embodiment of the invention disclosed herein is a methodcomprising the steps of: heat-treating an amorphous silicon film at atemperature lower than 600° C. to crystallize the amorphous siliconfilm; and irradiating the crystallized silicon film with laser light.This method is characterized in that during the laser irradiation, thesample is maintained within ±100° C. of the temperature of the heattreatment.

A third embodiment of the invention disclosed herein is a methodcomprising the steps of: heat-treating an amorphous silicon film tocrystallize it; implanting impurity ions into at least a region of thecrystallized silicon film; and irradiating the ion-implanted region withlaser light. This method is characterized in that during the laserirradiation, the sample is maintained within ±100° C. of the temperatureof the heat treatment.

A fourth embodiment of the invention disclosed herein is a methodcomprising the steps of: heat-treating an amorphous silicon film tocrystallize it; implanting impurity ions into at least a region of thecrystallized silicon film; and irradiating the ion-implanted region withlaser light. This method is characterized in that during the laserirradiation, the sample is maintained within ±100° C. of the temperatureof the heat treatment.

A fifth embodiment of the invention disclosed herein is a methodcomprising the steps of: irradiating an amorphous silicon film with alaser beam having a linear cross section while moving the laser beam insteps from one side of the amorphous silicon film to opposite side tocrystallize irradiated regions in succession. This method ischaracterized in that the laser irradiation is performed while heatingthe irradiated surface above 450° C.

In the fifth embodiment constructed as described above, the laser beamof the linear cross section is moved in steps and made to impinge on thefilm. Consequently, the required regions can be effectively irradiatedwith the laser light. Normally, the temperatures of irradiated surfacesare limited to about 600° C. However, these temperature are restrictedby the material of the substrate. Higher temperatures may also be used.

A sixth embodiment of the invention disclosed herein is a methodcomprising the steps of: introducing a metal element for promotingcrystallization into an amorphous silicon film; heat-treating theamorphous silicon film to crystallize it; and irradiating thecrystallized silicon film with laser light. This method is characterizedin that during the laser irradiation, the sample is maintained within±100° C. of the temperature of the heat treatment.

In the sixth embodiment constructed as described above and in thefollowing seventh through tenth embodiments, the metal element forpromoting crystallization is one or more elements selected from thegroup consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn, Ag, andAu. Among these metal elements, nickel is the element producing the mostconspicuous effect.

In the above-described configurations, the heat treatment temperaturecan be selected to lie within the range of from 450° C. to 750° C. Theupper limit of this temperature is restricted by the highest tolerabletemperature of the substrate. Where a glass substrate is used, the upperlimit is roughly 600° C. Where the productivity is taken intoconsideration, this temperature is preferably higher than 550° C.Accordingly, where a glass substrate is employed, the heat treatment ispreferably performed at a temperature of about 550° C.-600° C.

Furthermore, during the laser irradiation, the heat treatmenttemperature is preferably about 550-600° C. Heating starting from atemperature of about 450° C. can be put into practical use. Inconsequence, it is desired to heat the substrate within the temperaturerange of from 550° C.±100° C.

A seventh embodiment of the invention disclosed herein is a methodcomprising the steps of: introducing a metal element for promotingcrystallization into an amorphous silicon film; heat-treating theamorphous silicon film at a temperature lower than 600° C. tocrystallize it; and irradiating the crystallized silicon film with laserlight. This method is characterized in that during the laserirradiation, the sample is maintained within ±100° C. of the temperatureof the heat treatment.

An eighth embodiment of the invention disclosed herein is a methodcomprising the steps of: introducing a metal element for promotingcrystallization into an amorphous silicon film; heat-treating theamorphous silicon film to crystallize it; implanting impurity ions intoat least a region of the crystallized silicon film; and irradiating theion-implanted region with laser light. This method is characterized inthat during the laser irradiation, the sample is maintained within ±100°C. of the temperature of the heat treatment.

A ninth embodiment of the invention disclosed herein is a methodcomprising the steps of: introducing a metal element for promotingcrystallization into an amorphous silicon film; heat-treating theamorphous silicon film to crystallize it; implanting impurity ions intoat least a region of the crystallized silicon film; and irradiating theion-implanted region with laser light. This method is characterized inthat during the laser irradiation, the sample is maintained within ±100°C. of the temperature of the heat treatment.

A tenth embodiment of the invention disclosed herein is a methodcomprising the steps of: introducing a metal element for promotingcrystallization into an amorphous silicon film; irradiating theamorphous silicon film with a laser beam having a linear cross sectionwhile moving the laser beam in steps from one side of the amorphoussilicon film to opposite side to crystallize irradiated regions insuccession. This method is characterized in that the laser irradiationis performed while heating the irradiated surface above 450° C.

In the tenth embodiment constructed as described above, the laser beamof the linear cross section is moved in steps and made to impinge ondesired regions. Consequently, the desired regions can be effectivelyirradiated with the laser light. Normally, the temperatures ofirradiated surfaces are limited to about 600° C. However, thesetemperature are restricted by the material of the substrate. Highertemperatures may also be used.

A laser processing method according to an eleventh embodiment of theinvention consists of irradiating a silicon film formed on a glasssubstrate with laser light. This method is characterized in that duringthe laser irradiation, the silicon film is heated at a temperature whichis higher than 455° C. and lower than strain point of the glasssubstrate.

A laser processing method according to a twelfth embodiment of theinvention comprises the steps of: irradiating a silicon film formed on aglass substrate with laser light; and then heating the silicon film at atemperature which is higher than 500° C. and lower than strain point ofthe glass substrate. This method is characterized in that during thelaser irradiation, the silicon film is heated at a temperature which ishigher than 455° C. and lower than the strain point of the glasssubstrate.

A laser processing method according to a thirteenth embodiment of theinvention consists of irradiating a silicon film formed on a glasssubstrate with laser light. This method is characterized in that duringthe laser irradiation, the silicon film is heated at a temperature of550° C.±30° C.

A laser processing method according to a fourteenth embodiment of theinvention comprises the steps of: irradiating a silicon film formed on aglass substrate with laser light; and then heating the silicon film at atemperature of 550° C.±30° C. This method is characterized in thatduring the laser irradiation, the silicon film is heated at atemperature of 550° C.±30° C.

A laser processing method according to a fifteenth embodiment of theinvention comprises the steps of: forming a silicon film on a glasssubstrate; heating the silicon film up to a desired temperature; andirradiating the silicon film with laser light while maintaining thedesired temperature. This method is characterized in that the desiredtemperature is higher than 500° C. and lower than strain point of theglass substrate.

A laser processing method according to a sixteenth embodiment of theinvention comprises the steps of: forming a silicon film on a glasssubstrate; making a first heat treatment of said amorphous silicon filmto crystallize it; irradiating the crystallized silicon film with laserlight; and then making a second heat treatment of the silicon film. Thismethod is characterized in that one or both of the first and second heattreatments are made at a temperature which is higher than 500° C. andlower than strain point of the glass substrate. This method is alsocharacterized in that the laser irradiation step is performed whileheating the substrate at a temperature which is higher than 455° C. andlower than the strain point of the glass substrate.

A laser processing method according to a seventeenth embodiment of theinvention comprises the steps of: forming an amorphous silicon film on aglass substrate; introducing a metal element for promotingcrystallization of silicon into the amorphous silicon film; making afirst heat treatment of the amorphous film; then irradiating thecrystallized silicon film with laser light; and then making a secondheat treatment of the silicon film. This method is characterized in thatone or both of the first and second heat treatments are made at atemperature which is higher than 500° C. and lower than strain point ofthe glass substrate. This method is also characterized in that the laserirradiation step is performed while heating the substrate at atemperature which is higher than 455° C. and lower than the strain pointof the glass substrate.

In the laser processing methods according to the eleventh throughseventeenth embodiments described above, a silicon film formed on aglass substrate is irradiated with laser light. During the laserirradiation, the substrate is heated at a temperature which is higherthan 455° C. and lower than strain point of the glass substrate.

The silicon film formed on the glass substrate can be an amorphous orcrystalline silicon film directly formed on the glass substrate.Alternatively, an insulating film such as a silicon oxide film orsilicon nitride film is formed as a buffer film on the glass substrate.An amorphous or crystalline silicon film is formed on the buffer film.

The substrate is heated above 455° C. during the laser irradiation toenhance the annealing effect of the laser irradiation. The silicon filmis irradiated with laser light to impart energy to the silicon film.This energy crystallizes the silicon film, improves the crystallinity ofthe silicon film, or activates impurities contained in the silicon film.The heating is used together with the laser irradiation. This canenhance the effect of the laser irradiation.

We irradiated an amorphous silicon film with KrF excimer laser lighthaving a wavelength of 248 nm to crystallize the amorphous silicon film.This amorphous silicon film was formed on a buffer film of silicon oxidefilm, which was, in turn, formed on a glass substrate. FIG. 22 shows therelation of the Raman intensity (relative value) of the silicon film tothe energy density of incident laser light. The Raman intensity(relative value) is the ratio of the Raman intensity of the silicon filmto the Raman intensity of single-crystal wafer. It follows that as theRaman intensity (relative value) is increased, the crystallinity isimproved. It can be seen from the graph of FIG. 22 that a silicon filmof higher crystallinity is obtained by heating the substrate (sample)while irradiating it with laser light, if the intensity of the laserlight remains the same.

FIG. 23 shows the relation of the half-value widths (relative values) ofRaman spectra to the energy densities of incident light. The half-valuewidth of a Raman spectrum is the ratio of the width giving a half valueof the peak of the Raman spectrum to the width of the Raman spectrumobtained from the single-crystal wafer. It follows that as thishalf-value width is reduced, the obtained silicon film has highercrystallinity.

As can be seen from the graph of FIG. 23, a silicon film havingexcellent crystallinity is obtained by heating the film whileirradiating it with laser light at the same time. Our experiments haveshown that the temperature of the heating conducted simultaneously withthe laser irradiation is set higher than 455° C., preferably above 500°C. More preferably, the temperature is higher than 550° C. Where theheating is done above 500° C., conspicuous effects are obtained.

One method of heating the substrate can use a heater mounted in a holderor stage holding the substrate. Another method consists of heating theirradiated surface by infrared light or the like. Correctly, the heatingtemperature is the measured temperature of the irradiated surface.However, if slight error is tolerated, then the measured temperature ofthe substrate can be used as the heating temperature.

The heating done simultaneously with the laser irradiation is preferablycarried out below the strain point of the glass substrate, because thesubstrate is prevented from warping or shrinking in spite of theheating. For example, Corning 7059 glass which is often used as thesubstrate of an active matrix liquid crystal display has a strain pointof 593° C. In this case, it is desired to conduct the heat treatment ata temperature lower than 593° C.

Furthermore, it has been empirically known that during the laserirradiation, if the substrate is heated at a temperature of 550° C.±30°C., then desirable results arise.

Especially, if the silicon film is crystallized by heating before thelaser irradiation, then conspicuous results are obtained. In the laserprocessing method according to the sixteenth embodiment described above,the amorphous silicon film formed on the glass substrate is firstcrystallized by heating. Then, the crystallinity is further enhanced bylaser irradiation. Subsequently, the film is heat-treated. In this way,the defect density in the obtained silicon film is reduced.

In the laser processing method according to the seventeenth embodiment,a catalytic element for promoting crystallization of the amorphoussilicon film is introduced into the silicon film. Then, a heat treatmentis made to crystallize the amorphous film. The metal element forpromoting crystallization can be one or more elements selected from thegroup consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au.Especially, where nickel (Ni) is used, a crystalline silicon film can beobtained by performing a heat treatment at a temperature of 550° C.±30°C. for about 4 hours.

One method of introducing the above-described element consists offorming either a layer of the metal element or a layer containing themetal element in contact with the surface of the amorphous silicon filmby sputtering, evaporation, or CVD techniques. Another method ofintroducing the above-described element consists of applying a liquidsolution containing the metal element to the surface of the amorphoussilicon film and holding the metal element in contact with the surfaceof the amorphous silicon film.

The amount of the metal element introduced is so set that theconcentration of the metal element in the silicon film is 1×10¹⁶ cm⁻³ to5×10¹⁹ cm⁻³, for the following reason. If the concentration of the metalelement is less than 1×10¹⁶ cm⁻³, then the desired effect cannot beobtained. Conversely, if the concentration of the metal element is inexcess of 5×10¹⁹ cm⁻³, then the electrical characteristics of thesemiconductor, or the obtained crystalline silicon film, are impaired.That is, the electrical characteristics of the film acting as a metalbecome more conspicuous.

Nickel element was introduced into several samples of amorphous siliconfilm. The samples were heat-treated to crystallize them. In this way,crystalline silicon films were derived. The spin densities in the filmswere measured. The results are listed in FIG. 24. It can be understoodthat the spin density in each film is a measure of the defect density inthe film.

In FIG. 24, samples 1, 2, and 5 underwent only heat treatment afterintroduction of nickel element. Sample 3 underwent laser irradiation(LI) after heat treatment. Sample 4 underwent laser irradiation (LI)after heat treatment. Then, sample 4 was subjected to heat treatment. Ascan be seen from FIG. 24, sample 4 has the lowest spin density, it beingnoted that sample 4 underwent heat treatment after laser irradiation(LI).

In this way, heat treatment conducted after laser irradiation is quiteeffective in reducing the defect density in the film. If the temperatureof the heat treatment performed after the laser irradiation is set above500° C., then desirable results are produced. The upper limit of thetemperature is restricted by the strain point of the glass substrate.

A laser processing system according to an eighteenth embodiment of theinvention comprises: a conveyance chamber having a means fortransporting a substrate; a first heating chamber having a means forheating the substrate; a second heating chamber for heating thesubstrate; and a laser processing chamber having a means for directinglaser light to the substrate. The first heating chamber, the secondheating chamber, and the laser processing chamber are connected togethervia the conveyance chamber. In the first heating chamber, the substrateis heated at a desired temperature. In the laser processing chamber, thesubstrate which was heated in the first heating chamber is irradiatedwith the laser light while heated. In the second heating chamber, thesubstrate which was irradiated with the laser light in the laserprocessing chamber is heat-treated.

Examples of system having the above-described structure are shown inFIGS. 18-20. In FIG. 18, indicated by reference numeral 301 is aconveyance chamber having a means 314 (robot arm) for transporting asubstrate 315. Heating chambers 305 and 302 have means for heating thesubstrate. A laser processing chamber 304 has means for directing laserlight to the substrate.

A laser processing system according to a nineteenth embodiment of theinvention comprises a means for irradiating a substrate with laser lightand a means for rotating the substrate through 90 degrees. This systemis characterized in that the laser light has a linear cross section.

A laser processing system according to a twenty-first embodiment of theinvention comprises a means for irradiating a substrate with laser lightand a means for rotating the substrate through 90 degrees. This systemis characterized in that the laser light has a linear cross section, andthat this laser light of the linear cross section is scanned at rightangles to longitudinal direction of the cross section of the laser lightand directed to the substrate. The substrate is rotated through 90degrees by the rotating means. Thus, the laser light of the linear crosssection is scanned from an orientation differing by 90 degrees from theprevious orientation and directed to the substrate.

A laser processing system according to a twenty-second embodiment of theinvention comprises a means for irradiating a substrate with laser lightand a means for rotating the substrate. This system is characterized inthat the laser light has a linear cross section.

A laser processing system according to a twenty-third embodiment of theinvention comprises a means for irradiating a substrate with laser lightand a means for rotating the substrate. This system is characterized inthat the laser light has a linear cross section, and that this laserlight is scanned at right angles to longitudinal direction of the crosssection of the laser light and directed to the substrate. The substrateis rotated by the rotating means so that the linear laser light isscanned at an orientation different from the previous orientation anddirected to the substrate.

A laser processing system according to a twenty-fourth embodiment of theinvention comprises: a laser light-irradiating chamber having means forproducing laser light; a substrate-rotating chamber having a means forrotating a substrate; and a conveyance chamber connected to these twochambers and having a conveyance means for transporting the substrate.This system is characterized in that the laser light has a linear crosssection, and that the linear laser light is scanned at right angles tolongitudinal direction of cross section of the laser light and directedto the substrate. Once the substrate is irradiated with the laser light,the substrate is transported into the rotating chamber by the conveyancemeans and rotated by the rotating means. Then, the substrate is againtransported into the laser light-irradiating chamber by the conveyancemeans. The substrate is again scanned with the laser light but at anangle different from the angle at which the laser light was emittedpreviously.

Examples of laser processing system having the above-described structureare shown in FIGS. 18-20. Systems shown in FIGS. 18-30 have means forproducing laser light in a laser processing chamber 304. In FIG. 20,indicated by numeral 331 is a laser for emitting laser light. Also,there are provided means for rotating the substrate by 90 degrees in achamber indicated by 303. Laser light from the laser 331 has a linearcross section whose longitudinal direction is directed from the frontside of the sheet of FIG. 3 to the opposite side.

The substrate shown in FIG. 3 is placed on a stage 353. This stage ismoved in the direction indicated by 354 so that the linear beam isscanned at right angles to the longitudinal direction of the beam. Inthe configuration shown in FIG. 3, the laser beam is scanned relative tothe substrate by moving the substrate. Of course, the laser beam may bemoved.

The laser irradiation can be repeated at least twice such that thedirection of the scan of the linear laser beam is varied by 90 degreesfrom the direction of the previous scan. In this way, the whole desiredsurface can be uniformly irradiated with the laser light.

After the first laser irradiation step, the substrate is rotated through90 degrees inside the chamber 303. Then, the second laser irradiationstep is performed. This can enhance the uniformity of the effect of thelaser irradiation. Of course, this scan can be repeated plural times.

Furthermore, the substrate can be rotated through 30 degrees. Threelaser irradiation steps can be performed. Of course, the number of laserirradiation steps can be increased further. The angle through which thesubstrate is rotated can be set at will in view of the uniformity of thelaser irradiation.

The twenty-fifth aspect of the present invention comprises:

a step of introducing into an amorphous silicon film a metal elementwhich promotes the crystallization of the amorphous silicon film;

a step of heat treating the aforementioned amorphous silicon film tocrystallize the amorphous silicon film; and

a step of irradiating with laser light the silicon film crystallized atthe preceding steps;

wherein a sample is kept at a temperature within a range of ±100° C.from the temperature at the aforementioned heat treatment.

In the aforementioned structure (of all the aspects disclosed in thespecification), as a metal element promoting the crystallization, onekind of metal element or a plurality of kinds thereof can be selectedsuch metal elements such as Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn,Ag and Au. Of these metal elements, nickel is a metal element that canprovide the most conspicuous effect.

In the aforementioned structure, as a temperature at the time of heattreatment, a temperature in the range of from 450 to 750° C., C can beselected. An upper limit of this temperature is limited by the heatresistance temperature of the substrate. When a glass substrate is usedas the substrate, about 600° C. is considered to be the upper limit.Further, when the productivity is considered, it is desirable that thistemperature is 550° C. or more. Consequently, it follows that when theglass substrate is used, it is desirable to heat treat the glasssubstrate at about 550 to 600° C.

It is desirable to set the heating temperature at the time of laserlight irradiation to about 550 to 600° C. However, heating at atemperature of about 450° C. or higher is practical. Consequently, it ispreferable to heat the glass substrate at a temperature within the scopeof 550° C.±100° C.

Further, the twenty-sixth aspect according to the present inventioncomprises:

a step of introducing into an amorphous silicon film a metal elementwhich promotes the crystallization of the amorphous silicon film;

a step of heat treating the aforementioned amorphous silicon film at600° C. or less to crystallize the amorphous silicon film; and

a step of irradiating with laser light the silicon film crystallized atthe previous steps with a sample being kept at a temperature within arange of ±100° C. from the temperature at the time of the aforementionedheat treatment.

Further, the twenty-seventh aspect according to the present inventioncomprises:

a step of introducing into an amorphous silicon film a metal elementwhich promotes the crystallization of the amorphous silicon film;

a step of heat treating the aforementioned amorphous silicon film tocrystallize the amorphous silicon film;

a step of doping impurity ions into at least part of the silicon filmcrystallized at the preceding steps; and

a step of irradiating with laser light an area into which theaforementioned impurity ions are doped with a sample being kept at atemperature within a range of ±100° C. from the temperature at the timeof the aforementioned heat treatment.

Further, another aspects according to the present invention comprises:

irradiating with laser light having a linear beam configuration anamorphous silicon film into which a metal element which promotes thecrystallization of the amorphous silicon film is introduced by movingthe amorphous silicon film successively from one side of the amorphoussilicon film to other side; and

successively crystallizing an area irradiated with laser light;

wherein the aforementioned laser light irradiation is carried out byheating to 450° C. or more a surface free from laser light irradiation.

In the aforementioned structure, a necessary area can be effectivelyirradiated with laser light by successively moving a linear beam toirradiate the area with the linear beam. Further, the condition of thetemperature (heating temperature) on a surface to be irradiated withlaser light is that the temperature is normally limited to about 600° C.However, this temperature is limited by the material quality of thesubstrate. Otherwise, a much higher temperature may be set.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a laser processing system of Example 1 of thepresent invention;

FIG. 2 is a cross-sectional view of the laser processing system ofExample 1;

FIG. 3 is a cross-sectional view of the laser processing system ofExample 1;

FIG. 4 is a block diagram of the laser processing system of Example 1;

FIG. 5 is a ray diagram of the laser optical system of the laserprocessing system of Example 1;

FIGS. 6(A)-6(C) are cross-sectional views illustrating steps for forminga crystalline silicon film on a substrate according to Example 2 of theinvention;

FIGS. 7(A)-7(C) are cross-sectional views illustrating steps for forminga thin-film transistor according to Example 2;

FIGS. 8(A)-8(C) are cross-sectional views illustrating steps for forminga crystalline silicon film on a substrate according to Example 3;

FIGS. 9(A)-9(D) are cross-sectional views illustrating steps for forminga thin-film transistor according to Example 3;

FIGS. 10(A)-10(C) are cross-sectional views illustrating steps forforming a crystalline silicon film on a substrate according to Example 4of the invention;

FIG. 11 is a schematic block diagram of a liquid crystal displayaccording to Example 5 of the invention;

FIGS. 12(A)-12(D) are cross-sectional views illustrating steps forforming a crystalline silicon film on a substrate according to Example 6of the invention;

FIGS. 13(A)-13(D) are cross-sectional views illustrating steps forforming a crystalline silicon film on a substrate according to Example 7of the invention;

FIGS. 14(A)-14(C) are cross-sectional views illustrating steps forforming a thin-film transistor according to Example 7;

FIGS. 15(A)-15(D) are cross-sectional views illustrating steps forforming a crystalline silicon film on a substrate according to Example 8of the invention;

FIGS. 16(A)-16(D) are cross-sectional views illustrating steps forforming a thin-film transistor according to Example 8;

FIGS. 17(A)-17(D) are cross-sectional views illustrating steps forforming a crystalline silicon film on a substrate according to Example 9of the invention;

FIG. 18 is a top view of a laser processing system of Example 10 of theinvention;

FIG. 19 is a cross-sectional view of the laser processing system ofExample 10;

FIG. 20 is a cross-sectional view of the laser processing system ofExample 10;

FIG. 21 is a top view of a laser processing system of Example 11 of theinvention;

FIG. 22 is a graph indicating the relation (relative values) of theintensities of Raman spectra arising from amorphous silicon filmsirradiated with laser light to the intensities of the laser lightincident on the silicon film; and

FIG. 23 is a graph indicating the half-value widths (relative values) ofthe intensities of Raman spectra arising from amorphous silicon filmsirradiated with laser light to the intensities of the laser lightincident on the silicon film.

FIG. 24 is a list showing relation between the manufacturing conditionof the crystalline silicon film and the spin density of the crystallinesilicon film.

FIG. 25 is a top view of the apparatus for laser processing.

FIG. 26 is a sectional view of the apparatus for laser processing.

FIG. 27 is a sectional view of the apparatus for laser processing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

In Embodiment 1, there is shown an apparatus for laser processingaccording to the present invention. FIG. 1 shows a top view of theapparatus for laser processing. FIG. 2 shows a sectional view takenalong line A-A′ of FIG. 1. FIG. 3 shows a sectional view taken alongline B-B′ of FIG. 1. Further, FIG. 4 shows a block diagram of theapparatus for laser processing.

In FIGS. 1 to 3, reference numeral 101 denotes a carry-in and conveyancechamber for carrying in and conveying a substrate (sample). In thecarry-in and conveyance chamber, there is accommodated in a cassette 105a large number of substrates 100. On each of the substrates 100, asilicon film to be irradiated with laser light and a thin-filmtransistor in the midst of the fabrication step are formed. When thesubstrates are carried in and out of the substrate carry-in andconveyance chamber 101, the whole cassette 105 which accommodates thesubstrates 100 are moved.

Reference numeral 102 denotes a conveyance chamber for conveying thesubstrates in the apparatus. The conveyance chamber is provided with arobot arm for conveying the substrates one by one. This robot arm 106incorporates heating means and is designed to keep the substratetemperature (sample temperature) on a constant level even whileconveying the substrates.

Further, reference numeral 125 denotes an alignment means forpositioning the substrates, the means having a function of accuratelypositioning the robot arm with respect to the substrates.

A chamber denoted by reference numeral 103 is a chamber for irradiatingthe substrates with laser light. In this chamber, the laser light 108emitted from the apparatus 107 for laser light irradiation can beapplied to the substrates arranged on a stage 109 on which each of thesubstrates is to be placed via a synthetic quartz window 150. The stage109 is provided with means for heating the substrates. As designated byan arrow, the stage 109 has a function of moving in a one dimensiondirection.

The apparatus for laser light irradiation 107 has a function ofexciting, for example, KrF excimer laser, and incorporates an opticalsystem shown in FIG. 5. The laser light is formed into a linear beamhaving a width of from several mm to several cm and a length of tens ofcm by passing through the optical system shown in FIG. 5.

A chamber denoted by reference numeral 104 is a heating chamber forheating the substrates (samples), the chamber accommodating a largenumber of substrates 100. A large number of substrates 100 accommodatedin the heating chamber are heated to a predetermined temperature withheating means (resistance heating means). The substrates 100 areaccommodated on a lift 111. When needed, the lift 111 is moved up anddown so that the substrates can be conveyed by the robot arm 106 in theconveyance chamber 102.

Each chamber has a closed structure, and can assume a reduced pressurestate, or a high vacuum state by exhaust systems 115 to 118. Each of theexhaust systems is provided with individual vacuum pump 119 to 122respectively. Further, each chamber is provided with gas supply systems112 to 114 and 126 respectively for supplying required gas (for example,inert gas). Further, each chamber is provided with gate valves 122 to124 to heighten independently the air-tightness of each chamber.

Embodiment 2

In embodiment 2, there is shown an example in which the thin-filmtransistors are fabricated using a method for laser processing accordingto the present invention. FIG. 12 shows steps of fabricating thin-filmtransistors until a crystalline silicon film is obtained. In thebeginning, as shown in FIG. 12(A), a glass substrate 601 is prepared. Asilicon oxide film 602 is formed to a thickness of 3000 Å as a base filmon the surface of the glass substrate by the sputtering process. As theglass substrate, for example, Corning 7059 glass substrate can be used.

Next, an amorphous silicon film (a-Si film) 603 is formed to a thicknessof 500 Å by the plasma CVD or reduced pressure thermal CVD. Then, anextremely thin oxide film 604 is formed by the UV light irradiation inthe atmosphere of oxidation characteristics. This oxide film 604 is usedfor improving the moisture characteristics of a solution in thefollowing solution coating step. The thickness of the oxide film 604 maybe preferably set to about tens of angstroms (FIG. 12(A)).

Next, nickel (Ni) is introduced which is a metal element for promotingthe crystallization of the amorphous silicon film 603. Here, a nickelacetate solution is used to introduce nickel element into a surface ofthe amorphous silicon film 601. Specifically, a nickel acetate solutionwhich is adjusted to have a predetermined density of nickel is drippedto form a water film 605. Then a spinner 606 is used for performing spindrying operation thereby realizing a state in which nickel elementcontacts the surface of the amorphous silicon film. The introducedamount of nickel is controlled by adjusting the density of nickelelement in the nickel acetate solution. (FIG. 12(B))

Next, the amorphous silicon film 603 is crystallized by heat treatingthe amorphous silicon film 603 thereby providing a crystalline siliconfilm 607. The heat treatment at this time may be carried out at aheating temperature of about 450 to 750° C. However, when the problem ofheat resistance of the glass substrate is considered, the heat treatmentis required to be carried out at 600° C. or lower. Further, when thetemperature is 500° C. or lower, time required of the crystallization istens of hours or more, which is disadvantageous from the viewpoint ofproductivity. Here, in view of the problem of heat resistance of theglass substrate and the problem of heat treatment time, the substrate issubjected to four hour heat treatment at 550° C. Thus, the crystallinesilicon film 607 is obtained. (FIG. 12(C))

When the crystalline silicon film 607 is obtained by heat treatment, thecrystalline silicon film 607 is irradiated with laser light using theapparatus for laser light irradiation shown in FIGS. 1 to 3 to furtherpromote the crystallization of the crystalline silicon film 607. Anoutline of the steps of laser processing is shown hereinbelow. In thebeginning, a cassette 105 accommodating a large number of substrates(samples) having a state shown in FIG. 12(C) is accommodated in asubstrate carry-in and conveyance chamber 101. Then, each chamber isevacuated to produce a high vacuum state. Further, the gate valve is tobe completely closed. Then the gate valve 122 is opened, and onesubstrate 100 is taken out of the cassette 105 with the robot arm 106and is moved to the conveyance chamber 102. Then the gate valve 124 isopened and the substrate held in the robot arm 106 is conveyed to aheating chamber 104. At this time, the heating chamber 104 is to bepreliminarily heated so as to heat the substrate to a predeterminedtemperature.

After the substrate is carried into the heating chamber 104, the nextsubstrate is taken out of the cassette 105 and is conveyed to theheating chamber 104. By repeating the aforementioned operationpredetermined number of times, all the substrates accommodated in thecassette 105 are accommodated in the heating chamber 104. All thesubstrates accommodated in the cassette 105 are accommodated in theheating chamber 104 followed by closing the gate valves 122 and 124.

After a predetermined duration of time has passed, the gate valve 124 isopened, and the substrate heated to a predetermined temperature (here at500° C.) is drawn into the conveyance chamber 102 with the robot arm106. At this time, the substrate is kept at 500° C. during theconveyance by heating means incorporated in the robot arm 106. Then, thegate valve 124 is closed. Further, the gate valve 123 is opened and thisheated substrate is conveyed to a chamber 103 for irradiating thesubstrate with laser light. Then, the gate valve 123 is closed.

As the laser light, linear laser light is used. A predetermined area isirradiated with the laser light by moving the substrate stage 109 in thewidthwise direction of the linear laser light at a state shown in FIG.12(D). Here, in a state shown in FIG. 12(D), the substrate stage 109 ismoved to irradiate the substrate with laser light so that the laserlight sweeps the substrate from the right end of the substrate to theleft end thereof. Here, the transfer speed of the substrate stage 109 isset to 10 cm/min. In embodiment 2, the laser light is irradiated whilethe temperature of the substrate stage 109 is kept at 500° C.

After the completion of the laser light irradiation, the gate valve 123is opened, and the substrate held in the substrate holder is conveyed tothe conveyance chamber 102 with the robot arm 106, followed by closingthe gate valve 123. Then, the gate valve 122 is opened, and thesubstrate is accommodated in the cassette 105 in the carry-in andconveyance chamber 101. After this, the gate valve 122 is closed.

All the substrates accommodated in the heating chamber can be irradiatedwith laser light by repeating the aforementioned operation. After thecompletion of the irradiation of all the substrates with laser light,the substrates accommodated in the cassette 105 are taken out of thecarry-in and conveyance chamber 101 to the outside of the apparatustogether with the whole cassette accommodating the substrates.

As shown in FIG. 12(D), an active layer 701 of the thin film transistoris formed by promoting the crystallinity of the crystalline silicon filmby laser light irradiation followed by patterning the film.Incidentally, the extremely thin oxide film 604 is removed at this time.(FIG. 7(A))

Next, the silicon oxide film 702 which functions as a gate insulatingfilm is formed to a thickness of 1000 Å by the sputtering process or bythe plasma CVD. Then, an aluminum film containing 0.18 wt % of scandium(Sc) is formed to a thickness of 6000 Å by the vapor deposition process.Then, the film is patterned to form a gate electrode 703. When the gateelectrode 703 is formed, the gate electrode 703 is subjected to anodicoxidation in an ethylene glycol solution containing 5% of tartaric acidby using the gate electrode 703 as an anode. Thus, an aluminum oxidefilm 704 is formed. The thickness of the aluminum oxide film 704 is setto about 2500 Å. The thickness of the aluminum oxide film 704 determinesthe length of the offset gate area formed in the subsequent step ofimpurity ion doping.

Further, impurity ions (phosphorus ions here in this embodiment) aredoped into the active layer by the ion doping process or by the plasmadoping process. At this time, the gate electrode 703 and the oxide layer704 surrounding the gate electrode 703 serve as a mask so that impurityions are doped into areas 705 and 709. Thus, the source area 705 and thedrain area 709 are formed in self-alignment. Further, a channelformation area 707 and offset gate areas 706 and 708 are formed also inself-alignment.

Then, the source area 705 and the drain area 709 are recrystallized andthe doped impurity is activated by the laser light irradiation. Stronglight may be applied to the areas 705 and 709 in place of the laserlight irradiation. The irradiation of the source/drain areas 705 and 709with laser light is carried out by an apparatus shown in FIGS. 1 to 3.Further, in the laser light irradiation, the substrate is heated to 500°C.

After the completion of the annealing by the laser light irradiation, asilicon oxide film 710 is formed to a thickness of 7000 Å, as aninterlayer insulating film by the plasma CVD. Then, after a holedrilling step is carried out, a source electrode 711 and a drainelectrode 712 are formed by using an appropriate metal (for example,aluminum) or other appropriate conductive material. Lastly, in theatmosphere of hydrogen, the silicon oxide film is subjected to one hourheat treatment at 350° C. thereby completing a thin-film transistorshown in FIG. 7(C).

Embodiment 3

Embodiment 3 is an example in which a crystal is grown in a paralleldirection on a substrate by selectively introducing a metal elementpromoting the crystallization of an amorphous silicon film into part ofthe surface of the amorphous silicon film whereby a thin-film transistoris fabricated by using a silicon film whose crystal has grown inparallel to each other on this substrate.

FIG. 13 shows steps until a crystalline silicon film is obtained. In thebeginning, a silicon oxide film 602 is formed to a thickness of 3000 Å,as a base film on a glass substrate 601 by the sputtering process.Further, an amorphous silicon film 603 is formed to a thickness of 500Å, by the plasma CVD or by the low pressure thermal CVD. Then, in theatmosphere of oxidation characteristics, an extremely thin oxide film604 is formed on the surface of the amorphous silicon film 603. Then aresist mask 801 is formed by using a resist. The resist mask 801 isconstituted so that the surface of the amorphous silicon film (on whichan oxide film 604 is formed) in an area denoted by reference numeral 802is exposed. The area denoted by reference numeral 802 has a rectangularshape (slit configuration) having a longitudinal side in a depthwisedirection of FIG. 13. (FIG. 13(A))

Next, after a nickel acetate solution is coated to form a water film800, a spinner 608 is used for performing a spin drying operation. Inthis manner, there is realized a state in which nickel is arranged incontact with part 802 of the surface of the amorphous silicon filmpartially exposed by the resist mask 801. (FIG. 13(B))

Next, the resist mask 801 is removed, and the substrate is subjected tofour hour heat treatment at 550° C. At this step, nickel is diffusedfrom the area 802. At the same time, a crystal is grown in a directionparallel to the substrate as shown by an arrow 803. This crystallizationis performed by the progress of crystals in a needle-like, a column-likeor a branch-like configuration. As a result of this crystallization, acrystalline-silicon film is obtained in which crystals are grown in oneor two dimensions in a direction parallel to the substrate. Here, sincethe area denoted by reference numeral 802 has a slit-like configurationwith a longitudinal direction in the depthwise direction of FIG. 8, thecrystal growth proceeds approximately in one dimension in a directiondesignated by an arrow 803. Incidentally, the crystal growth is carriedout by about 50 to 200 μm in a direction indicated by an arrow 803.(FIG. 13(C))

The crystal growth by heat treatment proceeds in a needle-like, acolumn-like or a branch-like configuration. However, the photographicobservation under TEM (transmitting electron-beam microscope) shows thatan amorphous component remains between crystal grown branches (a gapbetween the branches). The aforementioned residual amorphous componentis crystallized and the crystallinity is further improved by annealingthe amorphous component by the laser light irradiation.

This annealing by the laser light irradiation can be performed in thesame manner as the embodiment. In this manner, a crystalline siliconfilm 607 in which the crystallinity is promoted can be obtained. (FIG.13(D))

Next, the crystalline silicon film 607 is patterned to provide an activelayer 701 as shown in FIG. 7(A). At this time, it is important that thestarting point of the crystal growth and the end point of the crystalgrowth do not exist in the active layer 701. The purpose thereof is toform an active layer by avoiding areas having a high density of metalelement because the density of the introduced metal element (nickel inthis case) is high at the starting point and the end point of thecrystal growth. This enables avoiding the instability of devices underthe influence of the metal element. (FIG. 14(A))

Next, the silicon oxide film 702 which functions as a gate insultingfilm is formed to a thickness of 1000 Å by the sputtering process or bythe plasma CVD. Next, an aluminum film containing 0.18 wt % of scandiumis formed to a thickness of 6000 Å by the electron beam vapordeposition. Then, the aluminum film is patterned to form a gateelectrode 703. When the gate electrode 703 is formed, the gate electrodeis subjected to anodic oxidation in an ethylene glycol solutioncontaining 5% of tartaric acid using the gate electrode 703 as an anodethereby forming an oxide layer 704 of aluminum. The thickness of theoxide layer 704 is set to be about 2500 Å. The thickness of the oxidelayer 704 determines the length of the offset gate area formed at thefollowing step of the impurity ion doping.

Further, impurity ions (phosphorus here in this embodiment) are dopedinto the active layer by the ion doping process or by the plasma dopingprocess. At this time, the gate electrode 703 and the oxide layer 704surrounding the gate electrode 703 serve as a mask to dope impurity ionsinto the areas 705 and 709. In this manner, the source area 705 and thedrain area 709 are formed in self-alignment. Further, the channelformation area 707 and the offset gate areas 706 and 708 are formed alsoin self-alignment. (FIG. 14(B))

Then, the apparatus for laser processing shown in FIGS. 1 to 3 are usedfor the laser light irradiation to recrystallize the source area 705 andthe drain area 709 and to activate the doped impurities.

After the completion of annealing by the laser light irradiation, thesilicon oxide film 710 is formed to a thickness of 7000 Å as aninterlayer insulating film by the plasma CVD. Then, after the holedrilling step is carried out, the source electrode 711 and the drainelectrode 712 are formed using an appropriate metal (for example,aluminum) and other appropriate conductive material. Lastly, in theatmosphere of hydrogen, the silicon oxide film 710 is subjected to onehour heat treatment at 350° C. to complete a thin-film transistor shownin FIG. 14(C).

In the thin-film transistor shown in Embodiment 3, since carriers movealong a direction of the growth of crystals that have grown in aneedle-like, a column-like or a branch-like configuration in onedimension, the transistor is affected by the crystal grain boundary atthe time of carrier transfer with the result that crystals can beobtained which have a large carrier transfer degree.

Embodiment 4

Embodiment 4 is characterized by forming a crystalline area which isregarded as a single crystal or a crystal extremely approximate to thesingle crystal by the laser light irradiation using a metal elementpromoting the crystallization of an amorphous silicon film followed byforming an active layer of a thin-film transistor by using the area.

FIG. 15 shows a step for forming a crystalline area which can beregarded as a single crystal or a crystal extremely approximate to thesingle crystal. In the beginning, a silicon oxide film 602 is formed asa base film on a glass substrate 601 to a thickness of 3000 Å by thesputtering process. Further, the amorphous silicon film 603 is formed toa thickness of 500 Å by the plasma CVD or the low pressure CVD. Then, inthe atmosphere of oxidation characteristics, the amorphous silicon filmis irradiated with UV light to form an extremely thin oxide film 604 ona surface of the amorphous silicon film 603. Then, the resist is used toform a resist mask 801. The resist mask 801 is constituted so that thesurface of the amorphous silicon film (on which an oxide film 604 isformed) is exposed in an area denoted by reference numeral 802. The areadenoted by reference numeral 802 has a rectangular shape (slitconfiguration) having a longitudinal side in the depthwise direction ofFIG. 10. (FIG. 15(A))

Next, after a nickel acetate solution is coated to form a water film800, a spinner 606 is used for performing a spin drying operation. Thus,there is realized a state in which a nickel is arranged in contact withthe part 802 of the surface of the amorphous silicon film partiallyexposed by the resist mask 801. Incidentally, there is shown in thisembodiment an example in which the resist mask 801 is used. However, asilicon oxide film or the like may be used as a mask. (FIG. 15(B))

Then, the resist mask 801 is removed to irradiate the film with laserlight by using the apparatus shown in FIGS. 1 to 3. In the laser lightirradiation, while the sample is heated to 500° C., the linear laserlight 810 is moved (swept) in a direction designated by referencenumeral 811 so that the backward direction of FIG. 10 constitutes alongitudinal direction. This transfer speed is set to an extremely slowone on the order of 1 mm to 10 cm/min. At this time, in the area denotedby reference numeral 812, a crystal nucleus or a crystalline area isformed by heating. The generation of the crystal nucleus or theformation of the crystalline area results from the action of nickelelement.

When the linear laser light is moved as denoted by reference numeral811, crystals are grown from an area 812 into which an extremely smallamount of nickel is introduced as denoted by reference numeral 813. Thecrystal growth denoted by reference numeral 813 proceeds from the area812 where the crystal nucleus or the crystal area is formed in epitaxialgrowth or in a state that can be regarded the epitaxial growth. (FIG.15(C))

This crystallization is carried out as a result of the melting of thearea irradiated with the laser light or by the epitaxial growth (or agrowth that can be regarded as the epitaxial growth) of crystals fromthe previously crystallized area to this melted area. This crystalgrowth successively proceeds as denoted by reference numeral 813 bymoving the linear laser light 810 as denoted by reference numeral 811.Further, since nickel which is a metal element promoting thecrystallization is deflected to an area in which silicon is melted,nickel element is concentrated at the tip of the crystal growth alongwith the progress of the crystallization denoted by reference numeral813. Consequently, in the central part of the crystalline area 814, thedensity of nickel can be lowered.

This step of the laser light irradiation will be explained hereinbelow.In the beginning, a cassette 105 which accommodates a large number ofsubstrates having a state shown in FIG. 15(C) is accommodated in thesubstrate carry-in and conveyance chamber 101. Then, each chamber isevacuated to produce a high vacuum state. Further, the gate valve isplaced in the completely closed state. Then, the gate valve 122 isopened, and one substrate 100 is taken out of the cassette 105 with therobot arm 106 and is transferred to the conveyance chamber 102. Then thegate valve 124 is opened and one substrate held in the robot arm 106 isconveyed to the heating chamber 104. At this time, the heating chamber104 is preliminarily heated to a predetermined temperature (500° C., C)so as to heat the substrate. After the substrate is carried in theheating chamber 104, the next substrate is taken out from the cassette105 with the robot arm 106 again and conveyed to the heating chamber104. By repeating the aforementioned operation a predetermined number oftimes, all the substrate accommodated in the cassette 105 areaccommodated in the heating chamber 104.

Then, after the lapse of a predetermined time, the gate valve 124 isopened, and the substrate heated to a predetermined temperature (500° C.here in this embodiment) is drawn out to the conveyance chamber 102 withthe robot arm 106. The substrate is kept at 500° C. during theconveyance by the heating means incorporated in the robot arm. Then thegate valve 124 is closed. Further, the gate valve 123 is opened and thisheated substrate is conveyed to the chamber 103 for the laser lightirradiation. Then, the gate valve 123 is closed.

As the laser light, linear laser light is used. A predetermined area ofthe substrate is irradiated with the laser light by moving the substratestage 109 in the width direction of the laser light. Here, in a state ofFIG. 12(D), the substrate is irradiated with the laser light by movingthe substrate stage 109 from the right side of the substrate shown inFIG. 12(D) to the left side thereof so that the laser light sweeps thesubstrate. The transfer speed of the substrate stage 109 is set to 1cm/min. In this embodiment, the substrate is irradiated with laser lightwhile maintaining the temperature of the substrate stage at 500° C.

After the completion of the laser light irradiation, the gate valve 123is opened, and the substrate held in the substrate holder is conveyed tothe conveyance chamber 102 with the robot arm 106. Then, the gate valve123 is closed. Next, the gate valve 122 is opened, and the substrate isaccommodated in a cassette 105 in the substrate carry-in and conveyancechamber 101. After this, the gate valve 122 is closed.

All the plurality of substrates accommodated in the heating chamber areirradiated with laser light by repeating the aforementioned operation.After the irradiation of all the substrate with the laser light iscompleted, the substrates accommodated in the cassette 105 are taken outfrom the substrate carry-in and conveyance chamber 101 to the outside ofthe apparatus.

In this embodiment, time elapsed from the carrying the first substrateinto the heating chamber 104 until the carrying the last substrate intothe heating chamber 104 is regarded as being equal to time elapsed fromtaking out the first substrate from the heat chamber 104 to start toconvey the substrate to the chamber 103 for laser light irradiationuntil taking out the last substrate to start to convey the substrate tothe chamber 103 for laser light irradiation. With such a procedure, timeduring which the substrate is held in the heating chamber can be thesame with respect to all the substrates.

On the substrate, an amorphous silicon film in which nickel element isintroduced is formed as shown in FIG. 15(C). At 500° C., a crystalnucleus can be easily generated in a short time. In an area where nickelelement is introduced, the crystallization easily proceeds.Consequently, setting to an equal value the time during which thesubstrate is held in the heating chamber 104 is important for obtaininga uniform crystalline silicon film.

In this manner, it is possible to obtain a single crystal, or an area814 that can be regarded as a single crystal. The area that can beregarded as the single crystal contains 10¹⁶ to 10²⁰ cm⁻³ of hydrogen.The area has a structure in which the internal defect is terminated withhydrogen. (FIG. 15(D))

This area can be regarded as a very large crystal grain. Further, thisarea can be further enlarged.

As shown in FIG. 15(D), in the case where the single crystal or the area814 that can be regarded as the single crystal, an active layer of thethin-film transistor is formed by using these areas. In other words, thesubstrate is patterned to form an active layer denoted by referencenumeral 701 in FIG. 16. Further, at the time of the patterning of thesubstrate, an extremely thin oxide film 802 is removed. Further, asilicon oxide film 702 which functions as a gate insulating film isformed to a thickness of 1000 Å by the sputtering process or by theplasma CVD. (FIG. 16(A))

Next, an aluminum film containing 0.18 wt % of scandium is formed to athickness of 6000 Å by the electron beam vapor deposition process. Then,the substrate is patterned to form a gate electrode 703. After the gateelectrode 703 is formed, the gate electrode 703 is subjected to anodicoxidation in an ethylene glycol solution containing 5% of tartaric acidby using the gate electrode as an anode thereby forming an aluminumoxide layer 704. The thickness of this oxide layer 704 is set to about2500 Å. The thickness of the oxide layer 704 determines the length ofthe offset gate area formed in the following step of impurity iondoping.

Further, impurity ions (phosphorus ions) are doped into the active layerby the ion doping process or by the plasma doping process. At this time,the gate electrode 703 and the oxide layer 704 surrounding the gateelectrode 703 serve as a mask to dope impurity ions into areas 705 and709. In this manner, the source area 705 and the drain area 709 areformed in self-alignment. Further, a channel formation area 707 andoffset gate areas 706 and 708 are formed in self-alignment. (FIG. 16(C))

Then, the laser processing apparatus shown in FIGS. 1 to 3 is used forthe laser light irradiation to recrystallize the source area 705 and thedrain area 709 and to activate the impurity.

After the completion of the annealing by the laser light irradiation,the silicon oxide film 710 is formed as an interlayer insulating film toa thickness of 7000 Å by the plasma CVD. Then, after a hole drillingstep is carried out, the source electrode 711 and the drain electrode712 are formed by using an appropriate metal (for example, aluminum) andother appropriate conductive material. Lastly, in the atmosphere ofhydrogen, the substrate is subjected to one hour heat treatment at 350°C. to complete a thin-film transistor shown in FIG. 16(D).

In the thin-film transistor shown in this embodiment, an active layer isconstituted by using a single crystal or an area that can be regarded asa single crystal. Thus, the crystal grain does not substantially existin the active layer. Thus, the thin-film transistor is constituted sothat the transistor is not affected by the crystal grain in theoperation.

The structure shown in this embodiment can be effectively used in thecase where a plurality of thin-film transistors arranged in a line areformed. For example, the structure can be used in the case where aplurality of thin-film transistors shown in FIG. 16(D) are fabricated atthe same time in one line in the depthwise direction of FIG. 16. Thestructure formed by the arrangement of such a large number of thin-filmtransistors in a line can be used in a peripheral circuit(shift-resistor circuit or the like) of a liquid crystal electro-opticalapparatus. Further, the thin-film transistor using a single crystal or acrystalline silicon film that can be regarded as a single crystal isuseful for use in an analog buffer amplifier or the like.

Embodiment 5

Embodiment 5 is an example in which a mechanism of crystallization bythe laser light irradiation is efficiently used to obtain a crystallinesilicon film (with favorable crystallinity) which is more similar to asingle crystal.

FIG. 17 shows the fabrication step of the embodiment. In the beginning,a base silicon oxide film 602 is formed to a thickness of 3000 Å on aglass substrate 601 by the sputtering process. Then, the amorphoussilicon film 603 is formed to a thickness of 500 Å by the plasma CVD orthe low pressure thermal CVD. Further, in the atmosphere of oxidationcharacteristics, the substrate is irradiated with UV light to form anextremely thin oxide film 604. Further, a silicon oxide film 815 isformed which constitutes the mask. This silicon oxide film 815 may beformed by the sputtering process or by the plasma CVD. The silicon oxidefilm 815 may be formed by using a coating solution for forming a siliconoxide film. This is a type which is cured by heating at about 100 to300° C. For example, OCD (Ohka Diffusion Source) solution manufacturedby Tokyo Applied Chemistry Co., Ltd. can be used. This silicon oxidefilm 815 has a slit-like configuration having a longitudinal directionin the depthwise direction of FIG. 12 in an area denoted by referencenumeral 802. The silicon oxide film 815 is constituted so that thesurface of the amorphous silicon oxide film 603 (on which the oxide film604 is formed) is exposed in this slit-like configuration area 802. Thisslit-like configuration area may be provided with a width of several μto tens of μ in a required length. (FIG. 17(A))

Next, a nickel acetate solution is coated on the silicon oxide film toform a water film 800. Then, the spinner 606 is used for performing aspin drying operation to realize a state in which nickel element isprovided on the surface of the amorphous silicon film 603 in contactwith the surface of the amorphous silicon film 603 via an oxide film 604in the area 802. (FIG. 17(B))

Then, as shown in FIG. 17(C), linear laser light 811 is applied to thesubstrate while moving (sweeping) in a direction denoted by referencenumeral 811. This linear laser light is molded into a configurationhaving a longitudinal side in the depthwise direction of FIG. 12 byusing an optical system shown in FIG. 5.

The irradiation of the substrate with the laser light 810 is performedby heating the sample at 500° C. and reducing the transfer speed to anextremely slow speed of about 1 mm to 10 cm/min. At this time, in thearea denoted by reference 812, a crystal nucleus or a crystalline areais formed by heating. The generation of this crystal nucleus and theformation of the crystalline area result from the action of nickelelement. The step of the laser light irradiation is the same asEmbodiment 4.

When the linear laser light is irradiated while moving the laser lightas shown by reference numeral 811, the area denoted by reference numeral812 is rapidly cooled after the laser light irradiation because thesilicon oxide does not on the surface. Since the amorphous silicon filmto which the laser light has moved is vertically sandwiched between theupper and lower silicon oxide films, there is no place to which heatescapes with the result that the amorphous silicon film is instantlyheated to a high temperature. This means that a cold area 812 having acrystal structure and a high temperature melted area exist. Naturally, asteep temperature gradient is generated between the two areas. Thus thecrystal growth is promoted by the action of the temperature gradient sothat the crystal growth that can be regarded as an epitaxial growthsuccessively proceeds as denoted by reference numeral 813. Then, asingle crystal or an area that can be regarded as a single area 814 canbe obtained.

A structure shown in embodiment 5 enables realizing the facilitation ofthe growth start at the starting point and forming partially a singlecrystal or an area that can be regarded as the single crystal.

In this manner, a single crystal or an area that can be regarded as thesingle crystal denoted by reference numeral 814 of FIG. 17(D) can beobtained. This single crystal or an area that can be regarded as thesingle crystal can be formed over a length of tens of μm, and a singlecrystal thin film transistor can be formed by using the area.

Embodiment 6

FIG. 11 shows an embodiment in which an active matrix type liquidcrystal display system with a faster speed is constituted according tothe present invention. The embodiment shown in FIG. 11 is an example inwhich a liquid crystal display is miniaturized, and reduced in weightand in thickness by fixing a semiconductor chip provided on a main boardof a normal computer on at least one of a pair of substrates of a liquidcrystal display having a structure in which a liquid crystal issandwiched between the pair of substrates.

FIG. 11 will be explained hereinafter. A substrate 15 is a substrate ofa liquid crystal display. On the substrate a TFT 11, a pixel electrode12′, an active matrix circuit 14 having a plurality of pixels providingan auxiliary capacity 13, an X decoder/driver, a Y decoder/driver, andXY branch circuit are formed of TFTs. The TFT according to the inventioncan be used.

Then, on the substrate 15, other chips are further mounted. Then, thesechips are connected to the circuit on the substrate 15 with the wirebonding process, the chip on glass (COG) process or the like. Referringto FIG. 11, a correction chip, a memory, a CPU and an input port arechips provided in this manner. In addition to these chips, various otherchips may be provided.

Referring to FIG. 11, the input port refers to a circuit for reading asignal input from the outside to convert the signal into an imagesignal. The correction memory refers to a memory peculiar to a panel foran input signal or the like corresponding to the characteristics of theactive matrix panel. In particular, the correction memory hasinformation peculiar to each pixel as a non-volatile memory andindividually corrects the information. In other words, when there is apoint defect in the pixel on the electro-optical apparatus, a signalcorrected in accordance with the point defect is sent to the pixelsurrounding the point thereby covering the point defect to obscure thedefect. Otherwise, when the pixel is dark as compared with thesurrounding pixels, a larger signal is sent by the pixel to provide thesame brightness as the surrounding pixel with the dark pixel. Since thedefect information differs from one panel to another, informationaccumulated in the correction memory differs from one panel to another.

The CPU and the memory has the same function as normal computers. Inparticular, the memory has an image memory which corresponds to eachimage as a RAM. These chips are all of the CMOS type.

In addition, at least part of the integrated circuits which are requiredmay be constituted with one aspect of the present invention to furtherheighten the thin film of the system.

As described above, the CPU and even the memory are formed on the liquidcrystal display substrate. Thus constituting an electronic apparatuslike a personal computer on one substrate is very useful inminiaturizing a liquid crystal display apparatus and to widen the scopeof application thereof.

The thin-film transistor which is fabricated according to the presentinvention can be used in a circuit which is required by a liquid crystaldisplay systematized as shown in the embodiment. In particular, it isextremely useful to use the thin-film transistor which is fabricated byusing a single crystal or an area that can be regarded as the singlecrystal in an analog buffer circuit or other required circuits.

Embodiment 7

In embodiment 7, there is shown an apparatus for laser processing usedin the practice of the invention. FIG. 25 shows a top view of theapparatus of laser processing. FIG. 26 shows a sectional view takenalong line A-A′ of FIG. 25. FIG. 26 shows a sectional view taken alongline A-A′ of FIG. 25. FIG. 27 shows a sectional view taken along lineB-B′ of FIG. 25.

Referring to FIGS. 25 to 27, a cassette receiving and feeding chamber201 is a chamber for receiving and feeding a cassette 202 and 302 foraccommodating a substrate, and the chamber 201 is provided with a robotarm 203.

The cassette 202 accommodates a large number of substrates on which asilicon film to be irradiated with laser light and a thin-filmtransistor in the fabrication step are formed. The substrates areconveyed one by one from the cassette 202 into the apparatus with therobot arm 203 to be irradiated with laser light. Lastly, the substratesthat have been irradiated with laser light are accommodated in thecassette 302 with the robot arm 203.

The carry-in and conveyance chamber 204 serves as means for carrying inand conveying the substrates from the cassette receiving and feedingchamber 201. A placement base 205 for placing the substrate is provided.This placement base 205 has an alignment function to align the substrateand robot arm position precisely.

Reference numeral 206 denotes a conveyance chamber for conveying thesubstrate into the apparatus, and a robot arm 27 for conveying thesubstrate one by one is provided therein. This robot arm 207incorporates heating means. The robot arm 207 is devised so that thetemperature during the conveyance of the substrate is kept at a constanttemperature (sample temperature).

Inside of the chamber 208 for laser light irradiation, a stage 209 isprovided which is movable in one-dimension direction along an arrow asshown in FIG. 26. On the top surface, a synthetic quartz window 210 isprovided. Incidentally, the stage 209 is provided with means for heatingthe substrate. The chamber 208 for laser light irradiation isconstituted to irradiate the substrates with laser light 211 emittedfrom the external apparatus 211 for laser light irradiation via asynthetic quartz window 210.

The apparatus 211 for the laser light irradiation has a function ofexciting, for example, KrF excimer laser light and incorporates anoptical system shown in FIG. 5. The laser light passes through anoptical system shown in FIG. 5 so that the laser light is formed into alinear beam having a width of from several millimeters to severalcentimeters and a length of several tens of centimeters.

Reference numeral 213 denotes a heating chamber for heating thesubstrate (sample). Reference numeral 313 denotes a gradual coolingchamber for gradually cooling the substrate (sample). The heatingchamber 213 and the gradual cooling chamber 313 have the same structure,respective chambers being provided with a lifts 214 and 314 movable inthe vertical direction, resistance heating means 215 and 315 for heatingthe substrate. On the lifts 214 and 314, the substrates 200 are stackedand accommodated with a predetermined space with each other. In thisstate, a large number of substrates 200 are heated or cooled to apredetermined temperature at the same time with the resistance heatingmeans 215 and 315. When the substrate is carried in and transferred fromthe heating chamber 213, the lifts are moved up and down so that thesubstrates can be carried in and conveyed from the conveyance chamber206 with the robot arm 207 in the conveyance chamber 206.

The carry-in and transfer chamber 204, the conveyance chamber 206 andthe chamber for the laser light irradiation, the heating chamber 213,and the gradual cooling chamber 313 have a sealed structurerespectively. The air-tightness of each chamber is further heightened byproviding the gate valves 216 to 220. The carry-in chamber 204, theconveyance chamber 206, the chamber 208 for the laser light irradiation,and the heating chamber 213 are connected to the vacuum pumps 226 to 230with exhaust systems 221 to 225, respectively. Each chamber can beformed in a reduced pressure state or in a high vacuum state. Furthereach chamber is provided with gas supply systems 231 to 235 forsupplying required gas (for example, inert gas).

In this embodiment, the cassette 202 accommodating a large number ofsubstrates (samples) (substrates having, for example, a state of FIG.12(C)), and an empty cassette 302 for accommodating substrates that havebeen irradiated with laser light. The gate valve 216 is closed, and thecarry-in and conveyance chamber 204, the conveyance chamber 206, thechamber 208 for the laser light irradiation, the heating chamber 213 andthe gradual cooling chamber 216 are formed into a high vacuum stateusing vacuum pumps 226 to 230. After the passage of predetermined time,the gate valve 216 is opened. One substrate is taken out from thecassette 202 with the robot arm 203 and is conveyed to the carry-in andconveyance chamber 204 to be placed on the placement base 205. The gatevalve 216 is closed, and the gate valve 217 is opened so that thesubstrate on the placement base 205 is conveyed to the conveyancechamber 206 with the robot arm 207 in the conveyance chamber 206. Thegate valve 216 is closed, the gate valve 217 is opened, and thesubstrate on the placement base 205 is conveyed into the conveyancechamber 206 with the robot arm 207 in the conveyance chamber 206. Thegate valve 217 is opened, and the substrate held in the robot arm 207 isconveyed to the heating chamber 213. At this time, the heating chamber213 is preliminarily heated so as to heat the substrate to apredetermined temperature.

The gate valve 217 is closed, the gate valve 216 is opened, and thesubsequent substrate is taken out from the cassette 202 in the cassettereceiving and feeding chamber 201 and conveyed to the carry-in andconveyance chamber 204, and then the subsequent substrate is conveyed tothe heating chamber 213 with the robot arm 207. All the substratesaccommodated in the cassette 202 are accommodated in the heating chamber213 by repeating the aforementioned operation predetermined number oftimes. Incidentally, to keep the vacuum state in chambers behind thecarry-in and conveyance chamber 204, the gate valve 216 and the gatevalve 217 are controlled so that the gate valves 216 and 217 are notopened at the same time. Further, the apparatus is constituted so thatwhen all the substrates accommodated in the cassette 202 areaccommodated in the heating chamber 213, the first substrate is heatedto a predetermined temperature.

When the last substrate is conveyed from the cassette 202 to the heatingchamber 213, the first substrate heated to a predetermined temperatureis taken out to the conveyance chamber 102 with the robot arm 207, andthe gate valve 219 is closed. At this time, the temperature of thesubstrate is kept even during the conveyance with the heating meansincorporated in the robot arm 207. This heated substrate is conveyed toa chamber 208 for the laser light irradiation and is placed on the stage209, and the gate valve 218 is closed.

The linear laser light 212 emitted from the apparatus for the laserlight irradiation is incident on the chamber 208 for the laser lightirradiation from a synthetic quartz window 210 so that the substrate onthe stage 209 is irradiated with the laser light. A predetermined areais irradiated with laser light by moving the stage 209 in a widthdirection of the laser light 212. For example, in a state shown in FIG.6(D), the substrate is irradiated with laser light by moving thesubstrate stage 109 from the right end of the substrate to the left endthereof so that the substrate can be scanned by the laser light.

After the completion of the laser light irradiation, the gate valve 218is opened, the substrate on the stage 209 is conveyed to a gradualcooling chamber 313 with a robot arm 207. Then the second substrate isconveyed to the chamber 208 for the laser light irradiation so that thesecond substrate is irradiated with laser light. Although thetemperature of this gradual cooling chamber 313 is set to a lower levelthan the counterpart of the heating chamber 213, it is constituted sothat no drastic temperature variation is generated for fear that thesubstrate might be damaged.

The aforementioned operation is repeated a predetermined number of timesso that all the substrates in the heating chamber 213 are irradiatedwith laser light followed by being successively conveyed to the gradualcooling chamber 313 to be cooled. The apparatus is constituted in such amanner that when the last substrate is conveyed to the gradual coolingchamber 313, the first substrate is cooled to an appropriatetemperature. At this time, the gate valve 217 is opened, the firstsubstrate is conveyed from the heating chamber 213 to the carry-in andconveyance chamber 204 with the robot arm 207 and is placed on theplacement base 205. When the gate valve 217 is closed and the gate valve216 is opened, the substrate on the placement base 205 is accommodatedin the cassette 302 with the robot arm 203. Then, after the gate valve216 is closed, the gate valve 217 is opened so that the second substrateis conveyed from the gradual cooling chamber 313 to the carry-in andconveyance chamber 204 with the robot arm 207. By repeating theaforementioned operation a predetermined number of times, all thesubstrates cooled in the gradual cooling chamber 313 are accommodated inthe cassette 302. The cassette as a whole is taken out of the apparatus.

In embodiment 7, time elapsed from the carry-in of the first substratein the heating chamber 213 up to the carry-in of the last substrate inthe heating chamber 213 is set to be equal to time elapsed from thetaking out the first substrate from the heating chamber 213 to start toconvey the first substrate to the chamber 208 for the laser lightirradiation up to the taking out the last substrate from the heatingchamber to start to convey the last substrate to the chamber 208 for thelaser light irradiation. In this manner, the time during which thesubstrates are held in the heating chamber can be set to an equal levelwith respect to all the substrates.

In this embodiment, the temperature can be controlled to cool thetemperature by providing a gradual cooling chamber 313 according toembodiment 1 shown in FIGS. 1 to 3. Consequently, even substrates thatare liable to be damaged under the influence of a rapid change intemperature can be safely cooled without any damage. Thus, the yieldratio of semiconductors can be improved. For example, the temperature ofthe heating chamber 213 and the stage 209 for the chamber 208 for thelaser light irradiation may be set to 500° C. while the temperature ofthe gradual cooling chamber 313 may be set to 200° C. When thetemperature of the gradual cooling chamber 313 is set to about 200° C.,no rapid change in temperature is provided to the substrate even whenthe substrate is conveyed to the cassette receiving chamber 201 at roomtemperature from the gradual cooling chamber 313. In this particularembodiment, the gradual cooling chamber 313 is used as a chamber forcooling the substrate, the chamber 313 can be used also as a chamber forheating the substrate.

Further, in this embodiment, heating, laser light irradiation, andcooling are carried out at the same time in the heating chamber 213, thechamber 208 for the laser light irradiation and the gradual coolingchamber 313, respectively. Thus, the time required for the laserprocessing can be shortened.

In accordance with the present invention, the crystalline siliconcrystallized by the introduction of the metal element promoting thecrystallization and the heat treatment is annealed by the laser lightirradiation while the sample is heated to a temperature ranging withinthe scope of ±100° C. from the temperature of the aforementioned heattreatment with the result that the crystallinity of the crystallinesilicon film is further heightened to provide a silicon film having afavorable crystallinity.

Further, impurity ions are doped into the crystalline silicon filmcrystallized by the introduction of the metal element promoting thecrystallization and heat treatment and the crystalline silicon film isannealed by the laser light irradiation while the sample is heated at atemperature within the range of ±100° C. from the temperature at thetime of the aforementioned heat treatment with the result that theformation of the impurity area can be effectively carried out.

Further, the amorphous silicon film is irradiated with linear laserlight from one side of the film to the other side thereof while beingheated to a temperature of 450° C. or more with the result that thecrystal growth can be successively carried out to form a single crystalor an area that can be regarded as the single crystal.

In particular, a single crystal or an area having a high crystallinity(an area which can be regarded almost as the single crystal) can beeasily formed in a state in which a metal element promoting thecrystallization is introduced into the amorphous silicon film. Further,at this time, the metal element can be deflected at the end of thecrystal growth by irradiating the crystalline silicon film with linearlaser light while moving the linear laser light with the result that thedensity of the metal element in the crystalline area can be reduced asmuch as possible.

EXAMPLE 8

In the present example, a thin-film transistor is fabricated by a laserprocessing method disclosed herein. FIGS. 6(A)-6(C) illustrate stepsperformed until a crystalline silicon film is obtained. First, as shownin FIG. 6(A), a glass substrate 601 is prepared. A silicon oxide film602 is formed as a buffer film on the surface of the substrate to athickness of 3000 Å by sputtering. For example, the glass substrate canconsist of Corning 7059 glass.

Then, an amorphous silicon (a-Si) film 603 is formed to a thickness of500 Å by plasma-assisted CVD or low-pressure CVD (LPCVD) (FIG. 6(A)).

Thereafter, the laminate is heat-treated to crystallize the amorphoussilicon film 603, thus obtaining a crystalline silicon film 607. At thistime, the heating temperature is about 450-750° C. However, where theheat resistance of the glass substrate is taken into account, it isnecessary to perform the heat treatment below 600° C. If the heatingtemperature is lower than 500° C., then it takes tens of hours tocomplete the crystallization step. This is disadvantageous to theproductivity. In the present example, in view of the heat resistance ofthe glass substrate and also in view of the time of the heat treatment,the heat treatment is conducted at 550° C. for 4 hours. In this way, thecrystalline silicon film 607 is obtained (FIG. 6(B)).

After obtaining the crystalline silicon film 607 by the heat treatment,laser light is directed to the film 607 by the use of the laserprocessing system shown in FIGS. 1-3 to promote crystallization of thecrystalline silicon film 607. This laser processing step is brieflydescribed below.

First, a cassette 105 holding a number of substrates (samples) assumingthe state shown in FIG. 6(C) is inserted into a substrateloading/unloading chamber 101. Each chamber is evacuated to a highvacuum. It is assumed that every gate valve is closed. A gate valve 122is opened to permit a robot arm 106 to take one substrate 100 from thecassette 105 and to transport the substrate into a conveyance chamber102. Then, another gate valve 124 is opened. The substrate held by therobot arm 106 is moved into the heating chamber 104, which has beenpreheated, to heat the substrate at a desired temperature.

After transporting the substrate into the heating chamber 104, the nextsubstrate is taken from the cassette 105 again by the robot arm 106 andmoved into the heating chamber 104. These operations are repeated agiven number of times. In this way, all the substrates held in thecassette 105 are received in the heating chamber 104. Then, the gatevalves 122 and 124 are closed.

After a lapse of a given time, the gate valve 124 is opened. Thesubstrate heated to the given temperature (500° C. in this example) isbrought into the conveyance chamber 102 by the robot arm. During themovement of this substrate, the substrate is maintained at 500° C. bythe heating means incorporated in the robot arm. Thereafter, the gatevalve 124 is closed. The gate valve 123 is opened. The heated substrateis conveyed into the chamber 103 for irradiating the substrate withlaser light. Then, the gate valve 123 is closed.

The laser light has a linear cross section. A substrate stage 109 ismoved laterally of the cross section of the laser light so that thelaser light illuminates a desired area. In this example, as shown inFIG. 6(C), the substrate stage 109 is moved in such a way that the laserlight is swept from the right end of the figure to the left end duringthe laser irradiation. It is assumed that the stage 109 moves at a speedof 10 cm/min. In the present example, the temperature of the stage 109is maintained at 500° C. during the laser irradiation.

After completion of the laser irradiation, the gate valve 123 is opened.The substrate held by the substrate holder is moved into the conveyancechamber 102 by the robot arm 106. Then, the gate valve 123 is closed.Thereafter, the gate valve 122 is opened. The substrate is inserted intothe cassette 105 inside the loading/unloading chamber 101. Then, thegate valve 122 is closed.

The operations described above are repeated to irradiate every substratereceived in the heating chamber with the laser light. After completionof these irradiation steps, the substrates received in the cassette 105are taken from the system one by one through the substrateloading/unloading chamber 101.

The crystallinity of the crystalline silicon film is promoted by laserirradiation, as shown in FIG. 6(C). Then, the film isphotolithographically patterned to form the active layer 701 of athin-film transistor (FIG. 7(A)).

Then, a silicon oxide film 702 acting as a gate-insulating film isformed to a thickness of 1000 Å by sputtering or plasma-assisted CVD.Subsequently, an aluminum film containing 0.18% by weight of scandium isformed to a thickness of 6000 Å by evaporation techniques. The aluminumfilm is photolithographically patterned to form a gate electrode 703.Thereafter, an anodization process is carried out in an ethylene glycolsolution containing 5% tartaric acid. In this process, the gateelectrode 703 is used as the anode. In this way, an aluminum oxide layer704 is formed to a thickness of about 2500 Å. This thickness of theoxide layer 704 determines the length of an offset gate region whichwill be formed by an impurity ion implantation step performed later.

As shown in FIG. 7(B), impurity ions (phosphorus ions in this example)are introduced into the active layer by ion doping or plasma dopingtechniques. At this time, the gate electrode 703 and surrounding oxidelayer 704 act as a mask. The impurity ions are lodged into regions 705and 709 indicated by the hatching. In this manner, the source region 705and the drain region 709 are formed by self-aligned techniques. Achannel formation region 707 and offset gate regions 706, 708 are formedagain by self-aligned techniques.

After the implantation, the laminate is irradiated with laser light torecrystallize the source region 705 and the drain region 709 and toactivate the implanted impurities. Instead of the laser light, intenselight may be irradiated. The laser light is made to fall on thesource/drain regions by the system shown in FIGS. 1-3. During this laserirradiation, the substrate is heated at a temperature of 500° C.

After completion of the annealing making use of laser irradiation, asilicon oxide film 710 is formed as an interlayer insulating film to athickness of 7000 Å by plasma-assisted CVD. Then, holes are formed. Asource electrode 711 and a drain electrode 712 are formed from anappropriate metal such as aluminum or from other appropriate conductivematerial. Finally, the laminate is heat-treated in a hydrogen ambient at350° C. for 1 hour. In this way, a thin-film transistor as shown in FIG.7(C) is completed.

EXAMPLE 9

In the present example, an amorphous silicon film is irradiated withlaser light to form either a single crystal or a region havingcrystallinity which can be regarded as very close to a single crystal.Using this region, the active layer of a thin-film transistor is formed.

FIGS. 8(A)-8(C) illustrate steps for forming either the single crystalor the region having crystallinity which can be regarded as very closeto a single crystal. First, a silicon oxide film 602 is formed as abuffer film on a glass substrate 601 to a thickness of 3000 Å bysputtering. An amorphous silicon film 603 is then formed to a thicknessof 5000 Å by plasma-assisted CVD or LPCVD (FIG. 8(A)).

Laser light is irradiated by the use of the system shown in FIGS. 1-3.During this laser irradiation, the sample is heated at a temperature of500° C. The laser light 810 has a linear cross section. The longitudinaldirection of this linear cross section is in the direction of the depthof the drawing. Crystal nuclei are formed in a region 812 or this region812 is crystallized by heating.

The laser light 810 is swept in the direction indicated by the arrow 811at a quite low speed of 1 mm to 10 cm/min. As the linear cross-sectionallaser light 810 is moved in the direction indicated by the arrow 811,crystals are grown as indicated by 813 from the region 812. In thisprocess, crystals are grown epitaxially or substantially epitaxiallyfrom the crystal nuclei or from the region 812 where crystals are formed(FIG. 8(B)).

This crystallization takes place as follows. The region irradiated withthe laser light is molten. Crystals are grown epitaxially orsubstantially epitaxially from the previously crystallized region towardthe molten region. As the linear laser light 810 is swept as indicatedby 811, the crystal growth progresses as indicated by 813(FIG. 8(C)).

The laser irradiation step is described in detail below. First, acassette 105 holding a number of substrates (samples), assuming thestate shown in FIG. 8(A) is inserted into a substrate loading/unloadingchamber 101. Each chamber is evacuated to a high vacuum. It is assumedthat every gate valve is closed. A gate valve 122 is opened to permit arobot arm 106 to take one substrate 100 from the cassette 105 and totransport the substrate into a conveyance chamber 102. Then, anothergate valve 124 is opened. The substrate held by the robot arm 106 ismoved into the heating chamber 104, which has been preheated (at 500°C.), to heat the substrate at a desired temperature.

After transporting the substrate into the heating chamber 104, the nextsubstrate is taken from the cassette 105 again by the robot arm 106 andmoved into the heating chamber 104. These operations are repeated agiven number of times. In this way, all the substrates held in thecassette 105 are received in the heating chamber 104.

After a lapse of a given time, the gate valve 124 is opened. Thesubstrate heated at the given temperature (500° C. in this example) isbrought into the conveyance chamber 102 by the robot arm 106. During themovement of this substrate, the substrate is maintained at 500° C. bythe heating means incorporated in the robot arm. Thereafter, the gatevalve 124 is closed. The gate valve 123 is opened. The heated substrateis conveyed into the chamber 103 for irradiating the substrate withlaser light. Then, the gate valve 123 is closed.

The laser light has a linear cross section. A substrate stage 109 ismoved laterally of the cross section of the laser light so that thelaser light illuminates a desired area. In this example, as shown inFIG. 8(B), the substrate stage 109 is moved in such a way that the laserlight is swept from the right end of the drawing to the left end duringthe laser irradiation. It is assumed that the stage 109 moves at a speedof 1 cm/min. In the present example, the temperature of the stage 109 ismaintained at 500° C. during the laser irradiation.

After completion of the laser irradiation, the gate valve 123 is opened.The substrate held by the substrate holder is moved into the conveyancechamber 102 by the robot arm 106. Then, the gate valve 123 is closed.Thereafter, the gate valve 122 is opened. The substrate is inserted intothe cassette 105 inside the loading/unloading chamber 101. Then, thegate valve 122 is closed.

The operations described above are repeated to irradiate every substratereceived in the heating chamber with the laser light. After completionof these irradiation steps, the substrates received in the cassette 105are taken from the system one by one through the substrateloading/unloading chamber 101.

In the present example, the time between the instant when the firstsubstrate is transported into the heating chamber 104 and the instantwhen the final substrate is carried into the heating chamber 104 is setequal to the time between the instant when the first substrate is takenfrom the heating chamber 104 and started to be moved toward the laserirradiation chamber 103 and the instant when the final substrate istaken from the heating chamber 104 and started to be transported towardthe laser irradiation chamber 103. As a result, every substrate is heldin the heating chamber for the same time.

The amorphous silicon film is formed on each substrate. At thetemperature of 500° C., crystal nuclei are easily formed in a short timeand crystallization progresses. Therefore, making uniform the times forwhich the substrate are respectively held in the heating chamber 104 isimportant for fabrication of uniform crystalline silicon films.

In this way, a region 814 which consists of a single crystal or can beregarded as a single crystal can be obtained as shown in FIG. 8(C). Thisregion 814 contains hydrogen atoms at a concentration of 10¹⁶ to 10²⁰cm⁻³. The internal defects are terminated by hydrogen atoms. This regioncan be regarded as a very large crystal grain. This region can befurther increased in size.

When the region 814 which consists of a single crystal or can beregarded as a single crystal is obtained as shown in FIG. 8(C), theactive region of a thin-film transistor is formed, using this region.That is, a patterning step is conducted to form the active region,indicated by 701 in FIG. 9(A). During this patterning step, extremelythin oxide film 802 is removed. A silicon oxide film 702 serving as agate-insulating film is formed to a thickness of 1000 Å by sputtering orplasma-assisted CVD (FIG. 9(A)).

Subsequently, an aluminum film containing 0.18% by weight of scandium isformed to a thickness of 6000 Å by electron-beam evaporation techniques.The aluminum film is photolithographically patterned to form a gateelectrode 703. Thereafter, an anodization process is carried out in anethylene glycol solution containing 5% tartaric acid. In this process,the gate electrode 703 is used as the anode. In this way, an aluminumoxide layer 704 is formed to a thickness of about 2500 Å. This thicknessof the oxide layer 704 determines the length of an offset gate regionwhich will be formed by an impurity ion implantation step performedlater (FIG. 9(B)).

Impurity ions (phosphorus ions in this example) are introduced into theactive layer by ion doping or plasma doping techniques. At this time,the gate electrode 703 and surrounding oxide layer 704 act as a mask.The impurity ions are lodged into regions 705 and 709. In this manner,the source region 705 and the drain region 709 are formed byself-aligned techniques. A channel formation region 707 and offset gateregions 706, 708 are formed again by self-aligned techniques (FIG.9(C)).

The laminate is irradiated with laser light through the use of the laserprocessing system shown in FIGS. 1-3 to recrystallize the source region705 and the drain region 709 and to activate the implanted impurities.

After completion of the annealing making use of laser irradiation, asilicon oxide film 710 is formed as an interlayer insulating film to athickness of 7000 Å by plasma-assisted CVD. Then, holes are formed. Asource electrode 711 and a drain electrode 712 are formed from anappropriate metal such as aluminum or from other appropriate conductivematerial. Finally, the laminate is heat-treated in a hydrogen ambient at350° C. for 1 hour. In this way, a thin-film transistor as shown in FIG.9(D) is completed.

The thin-film transistor in the present example has the active layerformed, using the region which consists of a single crystal or can beregarded as a single crystal. Therefore, substantially no crystal grainsexist in the active region. The operation of the thin-film transistorcan be prevented from being affected by the crystal grain boundaries.

The configuration of the present example can be effectively used where aplurality of thin-film transistors arranged in a row are formed. Forexample, the configuration can be utilized where a number of thin-filmtransistors are arranged in a row in the direction of the depth of thedrawing as shown in FIG. 9(D). This configuration consisting of a row ofthin-film transistors can be used in a peripheral circuit such as ashift register circuit for a liquid crystal display. These thin-filmtransistors using such a crystalline silicon film which consists of asingle crystal or can be regarded as a single crystal can beconveniently used in an analog buffer amplifier or the like.

EXAMPLE 10

In the present example, a crystalline silicon film which is closer to asingle crystal (has better crystallinity) can be efficiently obtained byskillfully making use of the mechanism of the crystallization induced bylaser irradiation.

FIGS. 10(A)-10(C) illustrate fabrication steps in the present example.First, a silicon oxide film 602 is formed as a buffer layer on a glasssubstrate 601 to a thickness of 3000 Å by sputtering techniques. Then,an amorphous silicon film 603 is formed to a thickness of 500 Å byplasma-assisted CVD or low pressure thermal CVD. Subsequently, a mask isformed from a silicon oxide film. This silicon oxide film may be formedby sputtering or plasma-assisted CVD. Also, the silicon-oxide film maybe formed, using a liquid which is applied to form a silicon oxide film.This liquid in the form of a solution solidifies when heated to about100-300° C. For example, OCD (Ohka diffusion source) solution preparedby Tokyo Ohka Kogyo Co., Ltd. can be used. This silicon oxide film 815has a slit in a region indicated by 802, the slit extending in thedirection of the depth of the drawing. A part of the surface of theamorphous silicon film 603 is exposed by the slit-like region 802. Thisslit-like region has a desired length and a width of several micrometersto tens of micrometers (FIG. 10(A)).

During the irradiation, the linear laser light is swept in the directionindicated by the arrow 811, as shown in FIG. 10(B). The cross section ofthis laser light is shaped into a form extending in the direction ofdepth of the drawing by the optics shown in FIG. 5.

When the laser light 810 is being emitted, the sample is heated at 500°C. The laser light is swept at a very low speed of approximately 1 mm to10 cm/min. At this time, crystal nuclei or a crystallized region isformed by heating in the region 812 indicated by the hatching.

During the laser irradiation, if the linear laser light is moved in thedirection indicated by the arrow 811, the region 812 is rapidly cooledafter the irradiation because no silicon oxide film exists on thesurface of the region 812. The amorphous silicon film swept by the laserlight is sandwiched between the upper and lower silicon oxide films.Therefore, heat can escape to nowhere. Hence, the film is momentarilyheated to a high temperature. In particular, a cool region 812 havingcrystalline structure coexists with a hot molten region. Of course, asteep temperature gradient exists between them. This temperaturegradient promotes crystal growth. As a result, crystal growth which canbe regarded as epitaxial growth progresses as indicated by 813. Inconsequence, a region 814 which consists of a single crystal or can beregarded as a single crystal can be obtained.

In the configuration of the present example, start of growth at thegrowth starting point can be facilitated. Consequently, a region whichconsists of a single crystal or can be regarded as a single crystal canbe formed in a part of the film.

In this way, a region 814 which consists of a single crystal or can beregarded as a single crystal as shown in FIG. 10(C) can be obtained.This region 814 can be made to have a length of tens of micrometers ormore. A single-crystal thin-film transistor can be fabricated, usingthis region.

EXAMPLE 11

In the present example, a thin-film transistor is fabricated, using thelaser processing method disclosed herein. FIGS. 12(A)-12(D) illustratemanufacturing steps performed until a crystalline silicon film isobtained. First, as shown in FIG. 12(A), a glass substrate 601 isprepared. A silicon oxide film 602 is formed as a buffer film on thesurface of the substrate to a thickness of 3000 Å by sputtering. Forexample, the glass substrate is made of Corning 7059 glass.

Then, an amorphous silicon (a-Si) film 603 is formed to a thickness of500 Å by plasma-assisted CVD or LPCVD. The laminate is irradiated withUV light in an oxidizing ambient to form an extremely thin oxide film604. This oxide film 604 improves the wettability of a liquid solutionin a solution application step which will be carried out later. Thethickness of this oxide film 604 is on the order of tens of angstroms(FIG. 12(A)).

Thereafter, nickel (Ni) which is a metal element for promotingcrystallization of the amorphous silicon film 603 is introduced. In thisexample, nickel element is introduced to the surface of the amorphoussilicon film 603, using solution of nickel acetate. More specifically,the solution of nickel acetate adjusted so as to obtain a desired nickelconcentration is dripped to form a water film 800. Then, a spin-dryingstep is performed, using a spinner 606. The nickel element is in contactwith the surface of the amorphous silicon film. The amount of theintroduced nickel is controlled by adjusting the concentration of nickelelement in the nickel acetate solution (FIG. 12(B)).

Subsequently, the laminate is heat-treated to crystallize the amorphoussilicon film 603. In this way, a crystalline silicon film 607 isobtained. At this time, the heating temperature is about 450-750° C.However, where the heat resistance of the glass substrate is taken intoaccount, it is necessary to perform the heat treatment below 600° C. Ifthe heating temperature is lower than 500° C., then it takes tens ofhours to perform the crystallization step. This is disadvantageous tothe productivity. In the present example, in view of the heat resistanceof the glass substrate and also in view of the time of the heattreatment, the heat treatment is conducted at 550° C. for 4 hours. Inthis way, the crystalline silicon film 607 is obtained (FIG. 12(C)).

Then, the crystalline silicon film 607 is irradiated with laser light bythe use of the laser processing system shown in FIGS. 1-3. This furtherpromotes the crystallization of the crystalline silicon film 607. Thelaser processing steps are carried out in the same way as in Example 2.

As shown in FIG. 12(D), the crystallinity of the crystalline siliconfilm is promoted by laser irradiation. A patterning step is performed inthe same manner as in Example 8 already described in connection withFIGS. 7(A)-7(C). Thus, the active layer of a thin-film transistor isformed. At this time, the extremely thin film 604 is removed. Using thisactive layer, the thin-film transistor is completed.

EXAMPLE 12

The present example relates to a laser processing system used to executethe present invention. FIG. 18 is a top view of the laser processingsystem of the present example. FIG. 19 is a cross-sectional view takenon line A-A′ of FIG. 18. FIG. 20 is a cross-sectional view taken on lineB-B′ of FIG. 18.

In FIGS. 18-20, indicated by reference numeral 306 is a loading chamberfor loading substrates (samples). The numerous substrates (samples) onwhich silicon films to be irradiated with laser light or unfinishedthin-film transistors are formed are received in a cassette 330. Underthis condition, the cassette 330 is inserted from the outside. Whensubstrates are inserted into the substrate loading chamber 306 from theoutside or they are withdrawn from the loading chamber, the substratesare moved together with the cassette holding them.

The substrates are moved inside the system by a conveyance chamber 301.This chamber is equipped with a robot arm 314 for transporting thesubstrates 315 one by one. The front end of the robot arm on which onesubstrate is placed can be rotated through 360 degrees and moved up anddown. This robot arm 314 also incorporates a heating means to maintainthe substrate temperature (sample temperature) constant duringconveyance of the substrate 315.

A substrate positioning alignment means 300 acts to precisely align therobot arm with the substrate. That is, the alignment means 300 maintainsconstant the positional relation between the robot arm and thesubstrate.

A laser irradiating chamber 304 irradiates the substrate with laserlight. In this chamber 304, laser light emitted by a laser 331 isreflected by a mirror 332 and directed to the substrate via a window 352made of synthesized quartz, the substrate being placed on a stage 353.This stage 353 is equipped with a means for heating the substrate andcapable of moving in one direction as indicated by the arrow 354.

The laser 331 can be a KrF excimer laser and is equipped with optics forshaping the cross section of the produced laser beam into a linear formas shown in FIG. 5. This linear cross section has a width of severalmillimeters to several centimeters and a length of tens of centimeters.The laser light is directed to the substrate (sample).

The longitudinal direction of this linear cross section of the laserlight is perpendicular to the direction of movement indicated by 354.That is, the longitudinal direction extends from the front side of thesheet of FIG. 20 to the rear side. The substrate is moved along with thestage 353 in the direction indicated by 354 while irradiating thesubstrate with this linear laser light. In this way, the whole substrateis scanned with the laser light.

Heating chambers 302 and 305 act to heat the substrate. The heatingchamber 305 heats the substrate (sample) before the laser light is madeto impinge on the substrate in the laser processing chamber 304. Theheating chamber 302 heat-treats the substrate after irradiated with thelaser light inside the laser processing chamber 304. A large number ofsubstrates 315 are stacked and received in each of the heating chambers302 and 305, as shown in FIG. 19. The held substrates 315 are heated ata desired temperature by heating means (resistive heating means) 317.The substrates 315 are received over a lift 316. As the need arises, thelift 316 is moved up and down. Required ones of the substrates can bemoved into and out of the heating chamber 305 one by one by means of arobot arm 314 inside a conveyance chamber 301.

A rotating chamber 303 acts to rotate each substrate through 90 degrees.A rotatable stage is installed in this rotating chamber 303. The desiredsubstrate is carried onto this stage by the robot arm 314, and then thisstage is rotated through 90 degrees. Thereafter, the substrate is takenout by the robot arm. In this way, the substrate is held by the robotarm while the substrate has been rotated through 90 degrees.

The substrate is irradiated with the laser light uniformly by the actionof the rotating chamber 303. As mentioned previously, the laser beamimpinging on the substrate (sample) has a linear cross section. Thesubstrate can be totally irradiated with the laser light by moving thesubstrate in one direction during the irradiation. In this case, thelaser light is scanned from one side of the substrate toward theopposite side. Then, the substrate is rotated through 90 degrees.Subsequently, the substrate is irradiated with the laser lightsimilarly. It follows that the laser light is scanned in two mutuallyperpendicular directions. Consequently, the substrate can be irradiatedwith the laser light uniformly.

An unloading chamber 307 acts to bring processed substrates out of thesystem, and has a cassette 330 holding the substrates in the same way asin the loading chamber 306. The numerous substrates are taken out of thesystem along with the cassette through a door 355.

The chambers 301, 302, 303, 304, 305, 306, and 307 described above areclosed vacuum vessels withstanding low pressures. These chambers havetheir respective evacuating systems. All of these chambers can assumereduced pressure condition. Each chamber has a system for supplying arequired gas such as nitrogen gas. Also, each chamber has an evacuatingsystem. If necessary, each chamber can be evacuated to a reducedpressure or a high vacuum. In FIG. 19, evacuating systems 318-319 areshown. In FIG. 20, evacuating systems 356, 1318, and 357 are shown.These evacuating systems are shown to have high-vacuum pumps 321-323,358, and 359.

These chambers are equipped with gate valves 310-313, 308, and 309 toassure the isolation and airtightness of each individual chamber.

An example of operation of the system shown in FIGS. 18-20 is describedbelow. An amorphous silicon film is formed on a glass substrate (10 cmsquare) made of Corning 7059 glass and having a strain point of 593° C.This amorphous silicon film is irradiated with laser light tocrystallize it. In this example, the amorphous silicon film iscrystallized by laser irradiation. The following sequence of operationcan be employed where the crystallized silicon film is furtherirradiated with laser light or where a silicon film doped with impurityions is annealed during formation of source/drain regions.

In the operations described below, it is assumed that the ambient ineach chamber shown in FIG. 18 is 1 atm. nitrogen ambient. In thisexample, a nitrogen ambient is exploited. Contamination level can bemost effectively reduced to a minimum by making each chamber have areduced pressure.

First, the gate valves 308-313 and the door 355 permitting access to theoutside are all closed. A required number of glass substrates eachhaving an amorphous silicon film formed thereon (hereinafter referredsimply to as the substrates) are inserted into a cassette (not shown).The cassette is carried into the loading chamber 306 together with thesubstrates. Then, the door (not shown) of the loading chamber is closed.Subsequently, the gate valve 312 is opened. One of the substrates heldin the cassette inside the loading chamber 306 is brought into theloading chamber 301 by the robot arm 314. At this time, the positionalrelation between the robot arm 314 and the substrate 315 is adjusted bythe alignment means 300.

The substrate 315 brought into the conveyance chamber 301 is receivedinto the heating chamber 305 by the robot arm 314. In order to put thesubstrate 315 into the heating chamber 305, the gate valve 311 is firstopened. Then, the substrate 315 is brought into the heating chamber 305by the robot arm 314. Subsequently, the gate valve 311 is closed.

In the heating chamber 305, the substrate is heated at a temperature of550° C. It is important that this temperature be set lower than thestrain point of the glass substrate, because if the heat treatment isperformed above the strain point, then shrinkage and deformation of theglass substrate will not be neglected.

After heating the substrate for a given time in the heating chamber 305,the substrate is transported into the conveyance chamber 301 by therobot arm 314. If the gate valves 308-313 are open, they must be closedwhen the substrate is carried by the robot arm in order to maintain theairtightness and cleanliness of each chamber.

The substrate taken from the heating chamber 305 is moved into the laserprocessing chamber 304. The amorphous silicon film formed on the surfaceof the substrate is irradiated with laser light. The robot arm isprovided with a heating means to permit the substrate to be transportedfrom the heating chamber 305 to the laser processing chamber 304 whilemaintaining the substrate at a temperature of 550° C. In the laserprocessing chamber 304, a heating means is mounted in the stage 353 onwhich the substrate is placed. During the laser irradiation, thesubstrate is kept at a temperature of 550° C.

The laser 331 produces a laser beam of a linear cross section. Thislaser beam is reflected by the mirror 332 and directed to the substratethrough a quartz window 352 formed in the laser processing chamber 304.

In this example, the stage 353 is moved in the direction indicated bythe arrow 354 so that the desired surface (i.e., the amorphous siliconfilm formed on the glass substrate) is totally irradiated with the laserlight. That is, the cross section of the laser beam extends from thefront side of the plane of FIG. 20 toward the opposite side. The laserbeam is scanned relative to the substrate in the direction indicated bythe arrow 354. In this way, the whole substrate surface placed on thestage 353 is scanned with the laser light.

For example, KrF excimer laser light having a wavelength of 248 nm canbe used as the above-described laser light. Also, an XeCl excimer laser,other excimer laser, or other means emitting coherent light can be usedas the laser 331. Furthermore, instead of laser light, a means foremitting intense light such as infrared light may be utilized.

After completion of the laser irradiation, the substrate is once broughtfrom the laser processing chamber 304 into the conveyance chamber 301 bythe robot arm 314. At this time, the gate valve 310 is first opened.Then, the substrate is brought into the conveyance chamber by the robotarm 314. Thereafter, the gate valve 310 is closed.

The substrate put in the conveyance chamber 301 is carried into thesubstrate rotating chamber 303, where the substrate is rotated through90 degrees. Any other operation is not done inside the rotating chamber303 and so the gate valve 309 can be kept open.

After rotating the substrate through 90 degrees in the substraterotating chamber 303, the substrate is brought into the conveyancechamber 301 again by the robot arm 314. Again, the substrate is movedinto the laser processing chamber 304. At this time, the orientation ofthe substrate placed on the stage 303 differs by an angle of 90 degreesfrom the orientation of the substrate assumed when the substrate isfirst transported into the laser processing chamber 304.

The laser light of the linear cross section is directed to the substratewhile moving the stage 353 again in the direction indicated by the arrow354. In this case, the direction of the scan of the laser light isdifferent from the direction of the first scan by 90 degrees.Consequently, the substrate can be uniformly irradiated with the laserlight. Hence, a uniformly crystallized silicon film can be obtained onthe glass substrate.

After the end of the second laser irradiation, the substrate is againtaken from the conveyance chamber 301 by the robot arm 314. Then, thesubstrate is conveyed into the heating chamber 302, where a heattreatment conducted at 550° C. produces desirable results.

After the substrate is heat-treated in the heating chamber 302, thesubstrate is brought into the conveyance chamber 301 by the robot arm314. Then, the substrate is received in the cassette 330 inside theunloading chamber 307. The operations described thus far aresuccessively conducted to accommodate substrates into the cassette 330inside the unloading chamber 307 in succession. When the cassette 330 isfilled up, the door 355 is opened. The substrates are taken out of thesystem together with the cassette 330. Thus, a series of laserirradiation steps is ended.

In the present example, two heating chambers are provided. In otherexamples such as Examples 3 and 8-11, laser annealing is performedduring fabrication of a crystalline silicon film. Then, the film isheat-treated to reduce the defect density in the silicon film. In thepresent example, these steps can be performed with one system because ofthe presence of the two heating chambers. Consequently, crystallinesilicon films having high crystallinity and low defect density can beobtained with high productivity.

Especially, a silicon film of better crystallinity can be obtained byapplying the present example to the fabrication steps for forming thecrystalline silicon film of Example 11 shown in FIGS. 12(A)-12(D) andthe crystalline silicon film of Example 3 shown in FIGS. 13(A)-13(D).Specifically, a metal element for promoting crystallization of anamorphous silicon film is selectively introduced into the surface of theamorphous silicon film to grow crystals parallel to the substrate. Then,the silicon film comprising these crystals is irradiated with laserlight to further enhance the crystallinity. If this film is thenheat-treated, a silicon film having good crystallinity and low defectdensity can be created.

EXAMPLE 13

The present example is a modification of the system shown in FIGS.18-20. FIG. 21 schematically shows the configuration of the presentexample. In both FIG. 18 (illustrating Example 12) and 21, likecomponents are indicated by like reference numerals. In the system shownin FIG. 21, a substrate is first heated in a heating chamber 305. Then,the substrate is irradiated with laser light in a laser processingchamber 304. Thereafter, the substrate is heat-treated in a secondheating chamber 351 to reduce the defects in the irradiated siliconfilm.

After completion of the heating in the heating chamber 351, thesubstrate is slowly cooled in a slow cooling chamber 350. The speed ofthe cooling is adjusted by adjusting the amount of nitrogen gasintroduced into the slow cooling chamber 350. Subsequently, thesubstrate is transported into an unloading chamber 307.

The laser irradiation of the present example can be employed forcrystallization of an amorphous silicon film, for annealing of a siliconfilm which was crystallized by heating (corresponding to the casesdescribed in Examples 11 and 3), and for annealing and activation of asilicon film doped with impurity ions.

A crystalline silicon film is crystallized by introduction of a metalelement for promoting crystallization and by heat treatment. Thecrystalline silicon film is annealed by laser irradiation while thesample is heated at a temperature that is within ±100° C. of thetemperature of the previous heat treatment. In this way, thecrystallinity is enhanced further. As a result, a silicon film havinggood crystallinity can be obtained.

A crystalline silicon film is crystallized by introduction of a metalelement for promoting crystallization and by heat treatment. Impurityions are implanted into the crystalline silicon film. Doped regions canbe effectively formed by annealing the substrate by laser irradiationwhile the sample is heated at a temperature that is within ±100° C. ofthe temperature of the previous heat treatment.

Crystals can be grown in succession by laser irradiation, i.e., bydirecting laser light having a linear cross section from one side of anamorphous silicon film toward the other side while heating the film at atemperature higher than 450° C. A region which consists of a singlecrystal or can be regarded as a single crystal can be formed.

Especially, after introducing a metal element for promotingcrystallization into an amorphous silicon film, regions of highercrystallinity which can be substantially regarded as a single crystalcan be readily formed by performing the above-described laserirradiation. At this time, the metal element can be made to segregate atthe points at which the crystal growth ends, by moving the laser beam ofthe linear cross section during the laser irradiation. As a result, theconcentration of the metal element in the crystallized regions can bereduced to a minimum.

In the novel laser processing method, a crystalline silicon filmcrystallized by heat treatment is heated at a temperature which iswithin ±100° C. of the temperature of the previous heat treatment. Underthis condition, the film is annealed by laser irradiation to furtherenhance the crystallinity. In this way, a silicon film having goodcrystallinity can be obtained. Impurity ions are implanted into asilicon film already crystallized by heat treatment. The film is heatedat a temperature which is within ±100° C. of the temperature of theprevious heat treatment. Under this condition, the film is annealed bylaser irradiation. In this way, doped regions can be effectively formed.

Furthermore, crystals are grown in succession according to laserirradiation by directing laser light having a linear cross section fromone side of an amorphous silicon film toward the other side whileheating the film at a temperature higher than 450° C. A region whichconsists of a single crystal or can be regarded as a single crystal canbe formed.

In the novel laser processing method, a metal element for promotingcrystallization is introduced into an amorphous silicon film. Under thiscondition, the above-described laser irradiation is conducted. Thus,regions of higher crystallinity which can be substantially regarded assingle crystals can be easily formed. After the laser irradiation, heattreatment is made. Therefore, defects caused by the laser irradiationcan be reduced.

During this laser irradiation, the laser light of a linear cross sectionis swept. In this way, the metal element can be caused to segregate atthe points at which crystal growth ends. The concentration of the metalelement in the crystallized region can be reduced to a minimum.

What is claimed is:
 1. A method of manufacturing a semiconductor devicecomprising: providing a semiconductor comprising amorphous silicon witha metal element which promotes the crystallization of the amorphoussilicon; irradiating laser light to the semiconductor; and heatannealing the semiconductor at a temperature of 500° C. or higher afterthe irradiating, subsequently heat annealing the semiconductor toterminate internal defects with hydrogen.
 2. The method of claim 1wherein an element or a plurality of elements selected from the groupconsisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn, Ag and Au areused as the metal element.
 3. A method of manufacturing a semiconductordevice comprising: providing a semiconductor comprising amorphoussilicon with a metal element which promotes the crystallization of theamorphous silicon; irradiating laser light to the semiconductor; andheat annealing the semiconductor at a temperature of 500° C. or higherafter the irradiating, subsequently heat annealing the semiconductor tohydrogenate the semiconductor, the concentration of hydrogen in thesemiconductor being 10²⁰ cm⁻³ or lower.
 4. The method of claim 3 whereinan element or a plurality of elements selected from the group consistingof Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn, Ag and Au are used as themetal element.
 5. A method of manufacturing a semiconductor devicecomprising: providing a semiconductor comprising amorphous silicon witha metal element which promotes the crystallization of the amorphoussilicon; implanting an impurity ion into at least a part of thesemiconductor; irradiating laser light to the part into which theimpurity ion is implanted by the implanting; heat annealing thesemiconductor at a temperature of 500° C. or higher after the laserlight irradiating; and subsequently heat annealing the semiconductor toterminate internal defects with hydrogen.
 6. The method of claim 5wherein an element or a plurality of elements selected from the groupconsisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn, Ag and Au areused as the metal element.
 7. A method of manufacturing a semiconductordevice comprising: providing a semiconductor comprising amorphoussilicon with a metal element which promotes the crystallization of theamorphous silicon; moving laser light having a linear beam configurationsuccessively from one side of the semiconductor to another side of thesemiconductor, to irradiate the laser light to a surface of thesemiconductor, heat annealing the semiconductor at a temperature of 500°C. or higher after the laser light irradiation, and subsequently heatannealing the semiconductor to terminate internal defects with hydrogen;wherein an area of the semiconductor irradiated with the laser light issuccessively crystallized.
 8. The method of claim 7 wherein an elementor a plurality of elements selected from the group consisting of Fe, Co,Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn, Ag and Au are used as the metalelement.
 9. The method of claim 7 wherein the metal element isselectively introduced into a predetermined area of the semiconductor.10. A method of manufacturing a semiconductor device comprising:producing laser light of a linear cross section; and directing saidlaser light to a surface of a semiconductor comprising amorphous siliconwhile moving said laser light from one side of said semiconductor to anopposite side of said semiconductor in succession; and heat annealingthe semiconductor at a temperature of 500° C. or higher after the laserlight directing, subsequently heat annealing the semiconductor toterminate internal defects with hydrogen.
 11. A method of manufacturinga semiconductor device comprising: providing a semiconductor comprisingamorphous silicon with a metal element which promotes thecrystallization of the amorphous silicon; implanting an impurity ioninto at least a part of the semiconductor; irradiating laser light tothe part into which the impurity ion is implanted by the implanting;heat annealing the semiconductor at a temperature of 500° C. or higherafter the irradiating, subsequently heat annealing the semiconductor tohydrogenate the semiconductor, the concentration of hydrogen in thesemiconductor being 10²⁰ cm⁻³ or lower.
 12. A method of manufacturing asemiconductor device comprising: providing a semiconductor comprisingamorphous silicon with a metal element which promotes thecrystallization of the amorphous silicon; moving laser light having alinear beam configuration successively from one side of thesemiconductor to another side of the semiconductor, to irradiate thelaser light to a surface of the semiconductor, heat annealing thesemiconductor at a temperature of 500° C. or higher after the laserlight irradiation, and subsequently heat annealing the semiconductor tohydrogenate the semiconductor, the concentration of hydrogen in thesemiconductor being 10²⁰ cm⁻³ or lower, wherein an area of thesemiconductor irradiated with the laser light is successivelycrystallized.
 13. A method of manufacturing a semiconductor devicecomprising: producing laser light of a linear cross section; anddirecting said laser light to a surface of a semiconductor comprisingamorphous silicon while moving said laser light from one side of saidsemiconductor to an opposite side of said semiconductor in succession;and heating annealing the semiconductor at a temperature of 500° C. orhigher after the laser light directing, and subsequently heat annealingthe semiconductor to hydrogenate the semiconductor, the concentration ofhydrogen in the semiconductor being 10²⁰ cm⁻³ or lower.
 14. A method ofmanufacturing a semiconductor device comprising: irradiating laser lightto a semiconductor comprising silicon and containing a metal elementwhich promotes the crystallization of the silicon; heat annealing thesemiconductor at a temperature of 500° C. or higher after theirradiating, and subsequently heat annealing the semiconductor tohydrogenate the semiconductor, the concentration of hydrogen in thesemiconductor being 10²⁰ cm⁻³ or lower.
 15. A method of manufacturing asemiconductor device comprising: irradiating laser light to asemiconductor comprising silicon and containing a metal element whichpromotes the crystallization of the silicon; heat annealing thesemiconductor at a temperature of 500° C. or higher after theirradiating, and subsequently heat annealing the semiconductor toterminate internal defect with hydrogen.
 16. A method of manufacturing asemiconductor device comprising: providing a semiconductor comprisingamorphous silicon with a metal element which promotes thecrystallization of the amorphous silicon; subsequently first heattreating the semiconductor to crystallize the semiconductor; irradiatinglaser light to the semiconductor after the first heat treating; secondheat annealing the semiconductor at a temperature of 500° C. or higherafter the irradiating; and third heat annealing the semiconductor afterthe second heat annealing to terminate internal defects with hydrogen.17. The method of claim 16 wherein said laser light is a linear laserlight.
 18. The method of claim 16 wherein said metal element is selectedfrom the group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn,Ag and Au.
 19. A method of manufacturing a semiconductor devicecomprising: providing a semiconductor comprising amorphous silicon witha metal element which promotes the crystallization of the amorphoussilicon; subsequently first heat treating the semiconductor tocrystallize the semiconductor; irradiating laser light to thesemiconductor after the first heat treating with the semiconductor beingkept at a temperature within a range of ±100° C. from a temperature atthe first heat treating; and second heat annealing the semiconductor ata temperature of 500° C. or higher after the irradiating; and third heatannealing the semiconductor after the second heat annealing to terminateinternal defects with hydrogen.
 20. The method of claim 19 wherein saidlaser light is a linear laser light.
 21. The method of claim 19 whereinsaid metal element is selected from the group consisting of Fe, Co, Ni,Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn, Ag and Au.
 22. A method of manufacturinga semiconductor device comprising: providing a semiconductor comprisingamorphous silicon with a metal element which promotes thecrystallization of the amorphous silicon; subsequently first heattreating the semiconductor to crystallize the semiconductor; implantingan impurity ion into at least a part of the semiconductor after thefirst heat treating; irradiating laser light to the part into which theimpurity ion is implanted by the implanting; second heat annealing thecrystallized semiconductor at a temperature of 500° C. or higher afterthe irradiating; and third heat annealing the semiconductor after thesecond heat annealing to terminate internal defects with hydrogen. 23.The method of claim 22 wherein said laser light is a linear laser light.24. The method of claim 22 wherein said metal element is selected fromthe group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn, Agand Au.
 25. A method of manufacturing a semiconductor device comprising:providing a semiconductor comprising amorphous silicon with a metalelement which promotes the crystallization of the amorphous silicon;subsequently first heat treating the semiconductor to crystallize thesemiconductor; implanting an impurity ion into at least a part of thesemiconductor after the first heat treating; irradiating laser light tothe part into which the impurity ion is implanted by the implanting withthe semiconductor being kept at a temperature within a range of ±100° C.from a temperature at the first heat treating; second heat annealing thecrystallized semiconductor at a temperature of 500° C. or higher afterthe irradiating; and third heat annealing the semiconductor after thesecond heat annealing to terminate internal defects with hydrogen. 26.The method of claim 25 wherein said laser light is a linear laser light.27. The method of claim 25 wherein said metal element is selected fromthe group consisting of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Zn, Agand Au.